The men's 400 metres hurdles at the 1984 Summer Olympics in Los Angeles, California had an entrylist of 45 competitors, with six qualifying heats (45 runners) and two semifinals (16) before the final (8) took place on Sunday August 5, 1984.
Edwin Moses won his second Olympic gold medal after 1976, while 18-year-old Danny Harris took the silver medal. Harald Schmid of West Germany took bronze
These were the standing World and Olympic records (in seconds) prior to the 1984 Summer Olympics.