The men's 400 metres was an event at the 1984 Summer Olympics in Los Angeles, California.

Gabriel Tiacoh won the Ivory Coast's first Olympic medal in any event, with a silver.

The favorites were Bert Cameron of Jamaica (winner of the first world championship in 1983) and Americans Antonio McKay and Alonzo Babers.

[2] The British Virgin Islands, Cameroon, Chad, Equatorial Guinea, the Gambia, Mauritius, Mozambique, Nepal, Oman, Rwanda, Somalia, Suriname, Togo, the United Arab Emirates, and Zimbabwe appeared in this event for the first time.

[2][4] In the UK TV show Little Britain, character Denver Mills is credited as having won the silver medal in the 400 metres at the 1984 Olympics.