The men's 400 metres hurdles at the 1984 Summer Olympics in Los Angeles, California had an entry list of 45 competitors from 30 nations, with six qualifying heats (45 runners) and two semifinals (16) before the final (8) took place on Sunday August 5, 1984. The maximum number of athletes per nation had been set at 3 since the 1930 Olympic Congress. American Edwin Moses won his second Olympic gold medal after 1976, while his 18-year-old teammate Danny Harris took the silver medal. Moses' gold was the United States' 13th victory in the event. Moses was the sixth man to win multiple medals in the event, and the second to win multiple golds. Harald Schmid of West Germany took bronze, giving that nation its first medal in the 400 metres hurdles since 1968.