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90K du Mont-Blanc: The Marathon du Mont-Blanc’s Toughest Race

May 18, 2026

5 min read

The Mont-Blanc 90K is the longest distance within the Mont-Blanc Marathon festival, a multi-race event attracting runners from around the world. Although it takes place in the same region as the UTMB® World Series Finals, it’s an independent event with its own history.

Location: Chamonix Valley, France
Distance: 55.92 miles (90 km)
Elevation gain: ~20,670 ft D+ (~6,300 m)
Event type: Alpine ultra-trail race
Part of / race series: Marathon du Mont-Blanc
Date: Late June
Participants: Maximum of 1,000

What is the 90K du Mont-Blanc?

The Mont-Blanc Marathon series began in 1979 with the 23km du Mont-Blanc. Other distances were added starting in 2003, and the first Mont-Blanc 90K took place in 2018.

Covering nearly 56 miles on and around the Mont-Blanc massif, this race combines ultra distance and alpine terrain, well beyond a typical trail run. Runners traverse forests, mountain passes, and exposed ridgelines above the Chamonix Valley, where trail running mental strength becomes just as important as physical endurance.

Marathon du Mont-Blanc: date and participants

The Mont-Blanc Marathon event occurs in late June each year, bringing runners to the Chamonix Valley for several days. The 2026 Marathon du Mont-Blanc is scheduled for June 25th-28th, with the 90K du Mont-Blanc on Friday, June 26th. Due to its demanding course, the 90K is limited to 1,000 runners.

The Marathon du Mont-Blanc races

The Mont-Blanc Marathon festival includes several distances:

Mont-Blanc 90K
Marathon (26.2 miles), with 8,956 ft elevation gain
23K (14.3 miles), the series’ oldest event
Duo Étoilé, a 13.1-mile team event ascending 4,757 ft at night, making nighttime trail running safety a priority

You can also sign up for the 10K (6.2 miles), a more approachable — though still technical — option with only 1,066 ft of elevation gain, or the highly technical KM Vertical, a true alpine race climbing 3,280 ft in just 2.4 miles. The Young Race and Mini-Cross provide options for younger athletes.

Together, these events accommodate runners of various levels and make up one of the most-established trail running gatherings in the Alps.

The Marathon du Mont-Blanc 90K route

The Marathon du Mont-Blanc route loops through the mountains surrounding the Chamonix Valley. For the 90K, runners start in town and quickly ascend the race’s highest peak, Le Brévent. This leads into the Aiguilles Rouges Nature Reserve, where runners traverse the distinctive red peaks that give the massif its name.

Across several more elevation changes, runners enter Switzerland and travel along Lac d'Émosson before looping back into France. The final major ascent leads to Signal Forbes and the Mer de Glace, before descending into Chamonix.

Why is the 90K Mont-Blanc so challenging?

The 90K Mont-Blanc’s distance, elevation changes, and technical terrain make it one of the more demanding trail races, mixing forest singletrack with steep alpine trails for hours-long climbs followed by technical descents. Training for trail running endurance and pacing awareness is essential.

Rocky paths and steep switchbacks demand focus and confident footwork. Altitude and exposure add another layer of challenge, increasing the risk of dehydration and bringing rapid temperature changes. Proper trail running layers and technical apparel are essential for staying comfortable in variable temperatures.

Photo credit: Enzo Besson

What does it take to run the 90K du Mont-Blanc?

Training for ultra-trail events like the 90K du Mont-Blanc requires mastering energy management to reach the finish.

Participants spend long stretches alone, making self-sufficiency vital and mountain trail experience a safety prerequisite. Steep alpine terrain requires trail running shoes with excellent traction. Experience also helps with selecting the right trail running gear — such as hydration vests — to keep you comfortable.

90K du Mont-Blanc FAQs

Despite its brief history, the 90K du Mont-Blanc already has a reputation as a test of grit and self-sufficiency.

How hard is the Mont-Blanc Marathon?

With multiple races available, the Mont-Blanc Marathon offers several difficulty levels. However, most races feature steep climbs and technical trails, and the 90K event is the most demanding.

Where does the 90K du Mont-Blanc start and finish?

The race starts and ends in Chamonix, France.

What is the Marathon du Mont-Blanc record for 90 km?

Despite a cutoff time of 24 hours, elite trail runners finish in well under 12. The current record of 10:23:11 was set in 2021 by Martin Kern.

The Marathon du Mont-Blanc series’ longest race

The 90K du Mont-Blanc is one of Europe’s defining alpine ultra-trail races. Pairing 56 miles with an ascent of over 20,000 ft, it delivers a grueling yet rewarding journey on and around the Mont-Blanc massif. This race embodies the essence of trail running in the Alps: steep climbs, technical trails, and a major sense of accomplishment at the finish.

Looking for world-class events across winter and mountain sports? Discover other races below:

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