Club drug use has become an area of concern among gay men and men that have sex with men, where circuit parties may attract tens of thousands of patrons, and where drug use and unsafe sex are not uncommon. Data were collected at three major gay circuit parties in North America in 1998-1999 in diverse geographical areas of the country. The estimated attendance of the 3 parties, all of which were held over holiday weekends, was respectively 25,000, 15,000, and 10,000. All data collection was based on a 2 page, 16-item questionnaire derived from 24 preliminary interviews with party patrons and previous research. The data indicate that reasons for gay circuit party attendance comprise two major dimensions: attendance for largely social reasons, and attendance for largely sensation-seeking reasons. The results suggest that drug use and sex are not associated with social reasons for circuit party attendance in any major way. Younger respondents were significantly more likely to report social reasons for attendance. Those that attend for largely sensation-seeking reasons are more likely to have used multiple drugs and to have reported sex on club drugs. They are also more likely to report unsafe sex over the past year. Drug use may facilitate unsafe sexual behaviors by decreasing both anxiety and self-observation, which may otherwise inhibit pleasurable sexual experiences. Targeting the small proportion of attendees that are attending specifically for reasons relating to sensation-seeking, including drug use and sexual contact, should be a priority. 1 figure, 2 tables, 5 references