42km du Mont-Blanc

The Race

History

The Marathon du Mont-Blanc festival is organised by the Club des Sports de Chamonix, a non-profit sports club with long roots in the valley, and the 42 km is its flagship marathon-distance race, the one the organiser markets as the weekend’s mythical race. The festival has grown well beyond a single event: alongside the 42 km it now runs a 90 km ultra, a 23 km, a 10 km, a Vertical Kilometre and other formats across the same June weekend.

Despite the word marathon and the familiar distance, the race bears little resemblance to a road marathon. The current course climbs and descends a combined 2,540 m across genuinely mountainous, technical terrain between Chamonix and the Swiss border area near Vallorcine, and it draws a strong international trail field every year. It sits at the accessible end of the sport’s major mountain races, in the sense that it is shorter than the ultras that share the valley.

That accessibility is relative and worth stating plainly. Road-marathon fitness alone is not a useful predictor of how a runner will cope with this course, and runner reports consistently describe the 42 km as considerably harder than the distance suggests. Technical descending, more than raw climbing ability, is the factor that most often separates a comfortable finish from a difficult one.

The course

The 42km du Mont-Blanc starts and finishes in central Chamonix and covers roughly 42 km of high-mountain trail with 2,540 m of combined ascent and descent, run semi-autonomously: runners carry mandatory safety and clothing kit and must be self-sufficient for water and nutrition between the course’s three full aid stations.

Three official checkpoints structure the race and its cutoffs: Le Tour at 13.5 km, Vallorcine at 23.5 km and La Flégère at 34.2 km. The single most demanding section is the climb over the Aiguillette des Posettes between Le Tour and Vallorcine, which the organiser identifies as the course’s main technical and physical challenge. The elevation record bears that out: the course sits between 1,041 m in Chamonix and 2,162 m at its high point, a band of 1,121 m, and the Posettes climb gains 670 m in just over four kilometres at an average above 15 per cent before losing more than 870 m on the far side at a similar gradient. Three further climbs of 100 m, 250 m and 450 m follow before the long descent home.

Checkpoint by checkpoint

Km 0 to 13.5: Chamonix to Le Tour. The race leaves Chamonix and heads up-valley to the first checkpoint at Le Tour, about 540 m above the start. The organiser describes this as comparatively fast and rolling by the standards of what follows, and the profile agrees: the gradients here run at 4 to 8 per cent with a couple of short descents in them. It is the single easiest place on the route to make a mistake, because it is the only part that rewards running hard and the only part where the cost of doing so is deferred.

Km 13.5 to 23.5: the Aiguillette des Posettes, and down to Vallorcine. This is the section the organiser identifies as the course’s central difficulty, and the numbers justify the framing. The climb gains 670 m in just over four kilometres, averaging above 15 per cent, which is sustained uphill hiking and not running for almost everybody in the field. The high point, 2,162 m, is the top. Then the course loses more than 870 m over the next five and a half kilometres down to Vallorcine, at a gradient just as steep in the other direction. Power-hiking the climb is what strong finishers do here. The descent is where the race is actually decided.

Km 23.5 to 34.2: Vallorcine to La Flégère. By Vallorcine the cumulative climbing and descending already matters more to the outcome of the day than the distance remaining. The ground to La Flégère climbs again in stages, roughly 100 m, then 120 m, then a 250 m pitch at around 16 per cent, then 450 m at 11 per cent, with sharp descents between them. Weather can shift meaningfully across this stretch, and conditions in the valley tell you very little about what is happening up here.

Km 34.2 to the finish: La Flégère back to Chamonix. The last section descends nearly 700 m over five kilometres back to the town, at around 14 per cent. Leg strength and coordination for sustained technical descending are still what is needed, and there is no fast freewheel to the line after everything already spent on the climbs. Runners who have saved something for this descent finish well; runners who emptied themselves on the Posettes do not.

There is no blue tangent line on a fixed single-track mountain course, and pacing by kilometre splits is the wrong mental model throughout. The three cutoffs at Le Tour, Vallorcine and La Flégère are the real pacing structure: plan your effort around clearing each one comfortably, adjusting for terrain and weather, and not around a finishing time.

Course Map

Up the valley to Le Tour, over the Aiguillette des Posettes to Vallorcine, across to La Flégère and back down to Chamonix. Tap a marker for the start and the three checkpoints, and scrub the slider or press play to move the orange marker along the course with the elevation profile beneath it.

Pacers

There are none, and a pace-group programme would make no sense on this terrain. Pace this race against the three checkpoint cutoffs and against the ground in front of you, adjusting for gradient and weather. Power-hiking the steep sections is normal practice among strong finishers here, not a sign of struggling.

What to wear

Late June in the Chamonix valley usually means genuine alpine summer at low altitude, with warm and sometimes hot conditions on the valley floor. That tells you almost nothing about conditions higher on the course. The ground towards Vallorcine and La Flégère runs colder and windier than the valley by a wide margin, and at 2,162 m the weather is a different proposition entirely. Snow on the high ground in late June is not unusual.

This overlaps directly with the mandatory kit requirement, which exists for exactly this reason: the organiser specifies mandatory clothing and safety equipment, the list is checked at bib collection, and it needs reconfirming each season instead of being assumed unchanged. In practice it means dressing and packing for a day that can hold valley heat and alpine cold within the same four or five hours, and carrying the difference.

Entry

Entry to the 42km du Mont-Blanc does not run through a single mechanism, which is why this page does not give it one label. The organiser splits the available bibs across several distinct routes. Ten per cent of places are reserved for Chamonix Valley residents. A direct-registration route is open to runners who commit to arriving by train or bus. Further places go through other registration and draw procedures, and a set of elite bibs is governed by UTMB Index and ITRA score thresholds.

The low-carbon emphasis carries through into a mandatory carbon contribution, calculated from each participant’s own return journey to Chamonix and payable as part of registration. Runners entering through the resident or train and bus routes upload proof of residence or of their travel commitment during the process. It is an unusually opinionated entry system, and it is worth reading the organiser’s own pages carefully: none of it works like a conventional marathon ballot.

Elite-bib thresholds have been published for a future edition, but general registration dates and pricing for the wider routes had not been published when this page was written. Given the hybrid structure and the resident and travel quotas involved, treat the opening of general entry as something to watch for, not a fixed date to plan around.

Fast Runner / GFA Standards

There is no Good For Age route in the conventional sense. The closest equivalent is the elite-bib pathway governed by UTMB Index and ITRA score thresholds, which functions as a performance qualification and not as an age-graded standard.

Race Weekend

Bib collection and the Trail Camp

Bib collection for the 42 km runs by appointment at EMC2 on Place du Mont-Blanc in central Chamonix. The most recent confirmed pattern, from 2026, ran Thursday 09:00 to 21:00, Friday 09:00 to 15:00 and Saturday 10:00 to 21:00. Photo identification and the full mandatory kit are needed at collection, because the kit is checked there rather than at the start line.

The festival’s Trail Camp functions as its expo and outdoor-industry village, set up around the same EMC2 site, which gives runners a chance to look at mountain-running equipment from festival partners while collecting a bib. Because the system is appointment-based and involves an equipment check, plan collection as a proper errand with time in it instead of a five-minute stop.

Race morning and mandatory kit

The 42 km starts in central Chamonix. The most recent confirmed edition used Place du Triangle de l’Amitié, and the finish returns to the same part of town. Staying within walking distance of the centre is the simplest option and removes the transport question from race morning entirely.

Because this is a semi-autonomous high-mountain race, the mandatory equipment list matters more here than on any road marathon on this site. The organiser’s regulations require, at minimum, a working mobile phone and water-carrying capacity of at least one litre, plus further mandatory clothing and safety kit specified in the current year’s rules. That list is checked at bib collection. Confirm it against the current regulations, and do not plan on buying missing items in Chamonix on the morning.

With only three full aid stations across the whole route, plus the finish, runners need to carry enough water and nutrition to cover the gaps between them, which is a kind of planning road-marathon runners are rarely asked to do. The maximum race time in 2026 was 10 hours, with intermediate cutoffs at each of the three checkpoints.

Aid stations

The 42 km carries three full aid stations plus the finish, at the three official checkpoints: Le Tour at 13.5 km, Vallorcine at 23.5 km and La Flégère at 34.2 km. That is a sparse spread against a road marathon’s water station every five kilometres, and it is the direct consequence of the semi-autonomous format: the gaps are yours to cover.

No detail on what is actually available at each station, brands, gels or hot food, was published when this page was written. Anyone planning a fuelling strategy in advance, or with particular nutrition needs, should treat the three stations as water and basic resupply points and carry everything else. Ten hours is a long time to be wrong about this.

Spectating

Chamonix is the easiest place to watch both the start and the finish, and for most visiting supporters it is the only realistic base for the day. The town sits on both ends of the race, needs no transport, and gives a genuine view of a very long day on the mountain. Plan for hours in between: this is a race where the leaders and the cutoff are separated by most of a working day.

Itinerary A, the town option. Watch the start in central Chamonix, spend the middle of the day in town where the cafés make the waiting easy, and return to the finish with generous time given the long cutoff window.

Itinerary B, La Flégère, lift permitting. Watch the start, then ride the cable car up to view the course at the 34.2 km checkpoint, provided the lift is confirmed running that day. Check operating hours and race-day access before travelling, and hold this plan loosely: the cable car is weather-dependent and this becomes Itinerary A if it is not running.

Itinerary C, the valley option. Watch the start, use a confirmed-running local lift or a short valley walk to a viewpoint over the Chamonix valley for the middle of the morning without relying on reaching the course itself, and return to town for the finish. This is the plan for a day when higher access is uncertain.

Lift operating hours, access restrictions and any race-day closures should be confirmed against the current year, since they change between editions.

After you finish

Central Chamonix holds a large concentration of restaurants, bakeries and bars within walking distance of the finish, so there is plenty of choice without travelling on legs that have just absorbed 2,540 m of climbing and descending.

Appetite and temperature regulation after a race of this profile differ meaningfully from after a road marathon. The combination of sustained climbing, technical descending and hours spent at altitude tends to leave runners colder than they expect and, for some, less immediately hungry. Plan for a warm layer at the finish and a meal an hour or two later.

Where to Stay

Stay in central Chamonix. The start, the finish and bib collection are all in the town, which makes this one of the simplest accommodation decisions on the site: anywhere within walking distance of the centre removes every transport question from race morning.

Central Chamonix

Central Chamonix is the recommendation without qualification. The 42 km starts and finishes here, bib collection is at EMC2 on Place du Mont-Blanc, and the Trail Camp is on the same site. Chamonix has an unusually deep range of accommodation for a town of its size, from hostels and refuges to full hotels, because it has been receiving mountaineers for a century and a half. A festival weekend of this scale still fills it.

Up the valley: Argentière and Le Tour

Argentière and Le Tour sit up-valley on the course itself, which makes them appealing and less convenient. They are quieter and often cheaper, and the valley bus and train connect them to Chamonix, but you are adding a transfer at the start of a ten-hour day and another at the end of it.

Down the valley: Les Houches and Servoz

The lower valley is the fallback when Chamonix has sold out, which for a festival weekend it does. It is cheaper, and the train up the valley is straightforward outside race hours. Check the first service of the morning against the start time before committing.

Vallorcine

Vallorcine holds the second checkpoint at 23.5 km and sits near the Swiss border at the far end of the valley. It is a genuine mountain village and a lovely place to stay for a week. As a race base it is the wrong end of the course, since the start and finish are both in Chamonix and race-day road access is what it is.

Booking timeline

Book Chamonix as soon as you have a bib, and not before. The entry structure here is hybrid enough that a place is not a formality: residents hold ten per cent, the train and bus route has its own commitment attached, and the rest runs through registration and draw procedures that had not opened when this page was written.

Once you do have a place, treat Chamonix accommodation as competitive. The festival spans several distances across one June weekend, which puts far more people in the valley than the 2,300 running the 42 km, and late June is the start of the alpine summer season regardless of the race. Rail to Chamonix via Geneva or Saint-Gervais is the low-carbon route the organiser actively rewards at entry, so book it early for the fare as well as the principle.

See & Do

Chamonix is the historic centre of alpinism and has more to do within a cable car ride of the finish line than almost any race destination on this site. Everything below starts in the town.

Aiguille du Midi

The cable car leaves from central Chamonix, a few minutes from the finish, and climbs to 3,842 m in two stages. It is one of the highest cable cars in the world and it puts you level with the Mont Blanc massif without a step of walking, which is the correct kind of sightseeing for the day after. Book a time slot in advance and take warm clothes: it is below freezing at the top in summer.

Mer de Glace and the Montenvers railway

The rack railway leaves from beside Chamonix station, about 0.5 km (0.3 miles) from the finish, and runs up to the Mer de Glace, the largest glacier in France. The ice cave at the bottom involves a substantial stair descent and re-ascent, so judge that against your legs; the view from the top station needs nothing.

Le Brévent and La Flégère

The Brévent cable car goes up from the town to 2,525 m on the opposite side of the valley from Mont Blanc, which is the side you want for the view of it. La Flégère, the same lift system, is where the race passed at 34.2 km, and walking a few hundred metres of that ground at your leisure is a strange and worthwhile thing to do the following day.

The town and the Musée Alpin

Chamonix has been a mountaineering town since the first ascent of Mont Blanc in 1786, and the Musée Alpin on Avenue Michel Croz covers that history. The centre is compact, flat and full of outdoor shops, which is the other reason people come.

Vallorcine and the Swiss border

About 18 km (11 miles) up the valley by the Mont-Blanc Express railway, which is a scenic narrow-gauge line in its own right. Vallorcine is where the race passed at 23.5 km, and the train carries on over the border to Martigny if you want to turn the afternoon into a proper excursion.

After the Race

There are no itinerary guides for this race yet. Chamonix is unusual among the destinations on this site in that the best things to do after the race are all within a lift ride of the finish line, which the See & Do section above covers, and the obvious longer trips out of the valley depend on a race date the organiser has not yet published.

What is worth saying now is the shape of it. Chamonix sits an hour and a half from Geneva, on a rail line that runs over the Swiss border to Martigny, and within reach of Annecy, Aosta through the Mont Blanc tunnel, and the Swiss Valais. Late June is the start of the alpine summer, so the high lifts and the mountain huts are opening for the season. Full itineraries will follow once the 2027 weekend is confirmed.