42km: a legendary event
Mont-Blanc 42km
With its 2540m vertical drop, the 42km du Mont-Blanc is the highlight of the weekend.
It brings together the best in the sport to wage a breathless battle in a dream setting! First on the fast, rolling trails of the first part of the race, then on the steep, technical slopes of the aiguillette des Posettes, the main difficulty of the course, before finishing facing the incredible panorama of the Mont Blanc range.
To take part in this race, it is recommended that you have good mountain running experience, are at ease on all types of terrain and are self-sufficient for several hours. We draw your attention to the fact that a runner with an UTMB performance index of less than 350 points has very little chance of completing the race, so it is recommended that you take part in another Mont Blanc Marathon event.
2025 race route
42 km semi-autonomous trail
2540m +/-
Open to Espoirs category and above
Limited to 2,300 runners
6 starting waves
Maximum time: 10 hours
3 full feed stations
1 finish refreshment station
Number withdrawal
Pick-up of 42km race numbers will be by appointment only, at the EMC2 space on Place du Mont-Blanc (Chamonix):
Thursday June 26, 2025 from 9am to 9pm,
Friday June 27, 2025 from 9am to 9pm,
Saturday June 28, 2025 from 9am to 9pm.
Runners must present photo ID and a race bag containing all compulsory equipment, to enable a timing chip to be fitted and equipment to be checked.
No bibs will be issued to runners without their compulsory equipment and identity papers. No race numbers will be distributed on Sunday morning before the start of the race.
Compulsory equipment
- Cell phone in working order.
- Minimum 0.50-liter water supply.
- Waterproof jacket with hood (gore-tex type) adapted to your size.
- Survival blanket (140cm x 200cm).
- Tumbler.
- Whistle.
- Cash.
Recommended equipment
- Cap.
- Tights.
- Gloves.
- Roll of straps.
- Bowl and spoon.
Time barriers
The time limits given below are for guidance only. In the event of adverse weather conditions, and for safety reasons, the organization reserves the right to stop the event in progress or modify the time limits. All decisions will be taken by the race jury.
A runner arriving at a time barrier after the deadline will be disqualified. The lower right-hand corner of the race number will be "cut out" by the station chief and the runner will be invited to return to Chamonix. Should the runner wish to continue on the course, his or her number will be collected by the station chief and the runner will no longer be considered a participant in the 42km du Mont-Blanc; he or she will therefore no longer be under the responsibility of the organizer. Anyone disrespecting the volunteers responsible for enforcing the time limits will be banned from all Mont Blanc Marathon events.
- Tour feed station (km 14): start time of last wave + 2h45.
- Vallorcine feed station (km 23.5): start time for last wave + 5.30 hrs.
- La Flégère feed station (km 34): start time for last wave + 8.30 hrs.
- Maximum race time - Chamonix finish (km 42): Start time for each wave + 10:00.
Maximum race time
Runners crossing the finish line after the maximum race time will not be classified and therefore not considered as finishers. This maximum time is calculated according to the start time of your wave.
42km du Mont-Blanc: maximum race time 10h00
Course description
After setting off from the Place du Triangle de l'Amitié in Chamonix (1035m), you gradually climb up the Chamonix valley, passing through the hamlets of Les Bois and Le Lavancher to reach Argentière (1250m). Runners bypass the village of Argentière and reach Le Planet via the Chemin des Rambles, before continuing along the small northern balcony to the village of Le Tour. From here, the route heads towards the Aiguillette des Posettes (2185m) along a path passing through the Chaleyre. The route then descends to the village of Vallorcine via the Col des Posettes (1997m) and the Plan de l'Envers path. From Vallorcine (1260m), you reach the hamlet of Le Buet, then take the Chemin des Diligences to the Col des Montets (1461m) in the heart of the Aiguilles Rouges nature reserve. Facing the Mont-Blanc chain, the path rises to La Flégère (1875m). After a balcony traverse to the combe de la Charlanon, you'll finish with a long descent on a lovely path that takes you back to Chamonix to finish the run on the Place du Triangle de l'Amitié.