Background: Sexual behaviours among HIV-positive male patients in Cambodia have not been fully evaluated. Objectives: The patterns of sexual behaviours and social factors were compared between married and single men. Methods: A retrospective cross-sectional survey of 174 male HIV patients was undertaken during March 1999–June 2000 in Phnom Penh. Results: Many participants (61%) reported that they were unaware that their sexual behaviours may have put them at risk of HIV infection. Sexual behaviours included having sex with a sex worker (90%), multiple sexual partners (41%), and both of these behaviours (37%). Two-thirds (69%) reported using a condom when having sex with a sex worker. Condom use with multiple sexual partners was low (24%). A history of condom use with a sex worker was less likely to be reported among married men than single men (P = 0.008). Always using condoms with a sex worker did not differ between married men and single men. Social factors that influenced visiting a sex worker included invitation by a friend (88%), alcohol consumption (74%), and having extra spending money (72%). Multivariate analysis suggests that alcohol consumption (P = 0.008) and having extra spending money (P = 0.02) were strongly associated with visiting a sex worker. Conclusions: In Cambodia, HIV-infected men frequently reported a history of using sex workers. Having multiple sex partners or using a sex worker and multiple sexual partners were not rare. Interventions should target men in settings where alcohol is consumed and to encourage married men to use condoms.