Water polo at the 2004 Summer Olympics took place at the Olympic Aquatic Centre where women competed for only the second time in the event at the Summer Olympics. Twelve teams competed in the men's event, where Russia was trying to avenge their defeat by Hungary at the Sydney Olympics. There were eight teams in the women's event, where holders Australia were hoping to retain the title. Men's teamsGroup A: , , , , and .Group B: , , , , and Women's teamsGroup A: , , and .Group B: , , and .