42km: the mythical race
42km du Mont-Blanc
With its 2540m elevation gain, the 42km du Mont-Blanc is the highlight of the weekend.
It brings together the best trailers in the discipline, engaged in a breathless battle in front of a dream setting! Firstly on the fast and rolling trails of the race beginning, then on the steep and technical slopes of the aiguillette des Posettes, the main difficulty of the course, to finish facing the incredible panorama of the Mont Blanc range.
To take part in this race, it is recommended to have good mountain running experience, to be comfortable on all types of terrain and to be self-sufficient for several hours. Please note that a runner with an UTMB index inferior to 350 points has very little chance to finish the race, so it is recommended to register for another Mont-Blanc Marathon race.
Race info
42 km semi-autonomous trail
2540m D+/-
Open to Espoirs category and above
Limited to 2,300 runners
6 starting waves
Maximum time: 10 hours
3 full refreshment points + 1 finish refreshment point
Bibs pick-up
Bibs pick-up for the 42km race will be possible 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 can be modified in the case of bad 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.
- 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.
A runner arriving at a time barrier point, after the time barrier has been applied, will be disqualified. The lower right-hand corner of the race number will be "cut out" by the station manager 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 Mont Blanc 90km, and 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.
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 10:00 a.m.
The organizers would like to draw runners' attention to the fact that, depending on the systems and settings used, GPX tracks may give different results for race distances and gradients.
