This study examined the demographics, substance use and sexual risk behaviours associated with group sex (GS) participation among a sample of club drug users (n = 498) in Miami. Men (n = 128; 46.3%) and women (n = 75; 33.7%) reported histories of GS. Group sex participation among men and women was associated with heroin and injection drug use, trading or selling sex, and sex while high, compared with no GS participation. Moreover, among men, GS was associated with buying sex and sex with an injection drug user; among women, GS was associated with substance dependence, a history of sexually transmissible infections and crack cocaine use, compared with no GS participation.