Mayhem '99 was the inaugural Mayhem professional wrestling pay-per-view (PPV) event produced by World Championship Wrestling (WCW), presented by Electronic Arts (in which the event was named after the EA-published video game of the same name) The event took place on November 21, 1999 from the Air Canada Centre in Toronto, Ontario, Canada.

Twelve matches were contested at the event, with the most notable feature being a thirty-two man tournament for the vacated WCW World Heavyweight Championship. The title had been vacated after previous champion Sting attacked a referee at Halloween Havoc and Goldberg defeated Sting for the title in an unsanctioned match. The first three rounds of the tournament took place on WCW television and the semi-final and final matches of the tournament were contested at Mayhem, where Chris Benoit defeated Jeff Jarrett and Bret Hart defeated Sting in the semi-final rounds. Hart defeated Benoit in the main event to win the final round and win the vacant title. A clip of the match appeared in the opening credits of the TV series Malcolm in the Middle.

Other featured matches on the card were Goldberg versus Sid Vicious in an "I Quit" match, Scott Hall versus Booker T for the WCW United States and World Television Championships and Filthy Animals versus The Revolution in an elimination match.