To describe the sociodemographic characteristics and sexual and drug use behaviors of men with AIDS who engage in bisexual activity.We interviewed 2120 men aged > or = 18 years who were reported with AIDS in 11 states and cities. Men were considered bisexual if they reported having had sex with a man and a woman in the previous 5 years.Of the 2020 men with AIDS who reported being sexually active in the previous 5 years, 1150 (57%) had had male partners only, 522 (26%) had had female partners only and 348 (17%) had had both. White men were least likely to report bisexual behavior (15%; 161 out of 1071). Men of Latin American descent were most likely to report bisexual behavior (24%; 37 out of 155), especially those born outside the United States who had lived there for < or = 10 years (38%; 11 out of 29). Bisexual Latin American men, regardless of birthplace, were more likely to be currently married than all other bisexual men (22 versus 7%; P < 0.05). HIV risk behaviors differed between men reporting bisexual and those reporting exclusively homosexual or heterosexual activity. Injecting drug use in the previous 5 years was more common among bisexual than homosexual men (12 versus 6%; P < 0.05). Bisexual men were more likely (P < 0.05) to have received money for sex (11%) than homosexual (4%) or heterosexual men (4%). This difference was even greater among injecting drug users receiving money for sex: bisexual (29%), homosexual (13%), heterosexual (3%).Demographics and HIV risk behaviors of bisexual men with AIDS differ from those of homosexual and heterosexual men with AIDS. These findings indicate that special efforts are needed to prevent sexual transmission of HIV among bisexual men.