The Grand Slam of Ultrarunning is a set of four of the most prestigious 100 mile races contested in the United States, comprising the Western States 100 in California, the Vermont 100 Mile Endurance Run in Vermont, the Wasatch Front 100 Mile Endurance Run in Utah, and the Leadville Trail 100 in Colorado. A small number of people manage to complete all four in one calendar year.
The term is also used for a successful completion of the 4 Deserts races, each of 250 kilometers, in one calendar year, a feat which has been managed by only 11 people.