The aim of this paper is to determine the sociodemographic characteristics of seronegative men engaging in behaviours at high risk for HIV transmission within a cohort of homosexual men. Eligible subjects in the cohort (n = 139) were those who were HIV negative and who completed an index visit between October 1989 and September 1990 and reported having sexual contact with casual partners during the previous 12-month period. Risk-takers (n = 31) were those who reported having unprotected anal receptive or insertive intercourse with casual partners; while the remaining subjects (controls) (n = 108) were those who reported either not engaging in anal intercourse with casual partners or using condoms when they did. Risk-takers were significantly younger and were more likely than controls to have incomes below $10,000, to smoke cigarettes and to use nitrite inhalants. Our findings suggest the importance of targeting AIDS prevention activities to specific subgroups within the gay community who are more at risk of HIV infection.