List of Isle of Man TT Mountain Course fatalities

This list is of fatal crashes on the Isle of Man TT Mountain Course used for the Isle of Man TT races, Manx Grand Prix and Classic TT races. The TT Course was first used as an automobile road-racing circuit for the 1908 Tourist Trophy event for racing automobiles, then known as the Four Inch Course. For the 1911 Isle of Man TT race motor-cycle races, the event was moved from the St John's Short Course to the Four Inch Course by the UK Auto-Cycle Club, and became known as the Isle of Man TT Mountain Course, or TT Course, when used for motorcycle racing.

Victor Surridge was the first fatality on the Isle of Man TT Mountain Course, after a crash at Glen Helen during practice for the 1911 Isle of Man TT races. This was possibly the first death in the Isle of Man in a motorcycle or road vehicle crash.

The deadliest year was 2005, when 10 people died: three riders and one marshal died during the June race, and six riders and one course bystander died during the Manx Grand Prix in August/September 2005. Since 1937, the only season without a fatality in either the TT or the Manx Grand Prix was in 1982. The 2012 and 2024, which are raced by more experienced professional riders, ended without fatalities, but there were fatalities in the Manx Grand Prix, which is raced with amateur riders except for the vintage motorcycle classes that experienced professionals may participate. The 2025 TT, which had its blue riband Senior TT cancelled because of weather, also ended without fatalities with the "amateur" season upcoming.