Les 40 bosses - Saint-Leu-la-Forêt 2026

Les 40 Bosses is a trail race series held in Saint-Leu-la-Forêt, within the Val-d'Oise department of Île-de-France. All events take place in the Montmorency forest. This winter weekend event offers five distances: 10 km Le Sprint, 20 km La Classique, 45 km L'historique, 75 km La Belle, and 120 km Le Monstre. The shortest race provides a forest trail option for those not wanting an ultra, while the longest presents a significant mountain-style challenge, even though it is located near Paris. The 120 km Le Monstre features 4,900 metres of elevation gain and consists of just two loops. The 75 km loop covers the entire forest massif. The 20 km and 45 km races often fill rapidly once registration opens, indicating the popularity of these middle distances. Sold-out races implement a waiting list system: when a runner withdraws, the next person on the list receives an email with a 48-hour deadline to accept the spot. Bib resale is prohibited, and any bib transferred through unofficial means will be invalidated.