At the 2004 Summer Olympics, the triathlon events were held at the Vouliagmeni Olympic Centre. Fifty triathletes contested the female event on August 25, and the same number contested the male event on August 26, making up a total of 100 competitors.

Triathlon at the Games of the XXVIII Olympiad
Venue	Vouliagmeni Olympic Centre
Dates	25–26 August 2004
Competitors	100 from 34 nations
← 2000 2008 →

Each competitor starts the event with a 1500-metre swim course, followed by a 40 kilometre road bicycle race and finish with a 10 kilometre road run. Both leg transitions (swimming—cycling and cycling—running) are performed on a special transition area, under judge's scrutiny and the duration of the transition is added to the final time.

A pre-Olympic test event was staged over the Olympic course in October 2003, and saw Denmark's Rasmus Henning and Australia's Michellie Jones winning the men's and women's events.