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.

However, when the Olympics returned in 1920 after World War I, the men's 400 metres hurdles was back and would continue to be contested at every Games thereafter.

Also returning was 1976 gold medalist Edwin Moses of the United States, who had not competed in 1980 due to the American-led boycott.

Moses had not lost a 400 metres hurdles race since 26 August, 1977; he had won 89 consecutive finals since then, including the inaugural 1983 World Championship.

[2] The Bahamas, Bahrain, Cameroon, Egypt, the Ivory Coast, Jamaica, Mozambique, Paraguay, Rwanda, the Seychelles, and the United Arab Emirates each made their debut in the event.