The "rave" phenomenon—loud music, flashing lights, and frenzied all-night dancing—has been a major element in the resurgence of psychedelic drug use in Western society.1 Purportedly central to raves is the use of "club drugs," including 3,4-methylenedioxy-methamphetamine, also called MDMA or ecstasy.1 The use of ecstasy seems to be increasing worldwide, with rave attendees being a high-risk population. Because these drugs have potentially serious physical and psychological consequences, such as anxiety, memory loss, paranoia, depression, cognitive impairment, cardiac complications, and kidney failure,2,3 the rave phenomenon has sparked the attention of health officials and policy makers. However, to our knowledge, no studies have collected self-report or objective drug use information from rave attendees in the United States.