The present study describes complex drug and sexual risk in a group of male sex workers (n = 79) who were recruited in the context of a larger study of young heroin users in Hanoi, Vietnam (n = 1270). Male sex workers were significantly more likely than male non-sex workers to be migrants (P < 0.001) and to have unstable housing (P < 0.001), to have lifetime exposure to marijuana (P < 0.001), 3,4 methylenedioxymethamphetamine (MDMA, ecstasy) (P < 0.01), amphetamines (P < 0.05), cocaine (P < 0.01) and morphine (P < 0.001). Male sex workers are more likely to currently use MDMA (P < 0.05), amphetamines (P < 0.001), morphine (P < 0.05) and to 'smoke' as their most frequent mode of heroin administration (P < 0.01). Male sex workers are more likely to have both male and female concurrent sex partners (P < 0.001), to have a history of sexual victimisation (P < 0.001), to have had more than three different sex partners in the past 30 days (P < 0.001), and to have had partners who injected drugs before sex (P < 0.001) or who used drugs during sex (P < 0.01). In their last sexual encounter with a client partner, approximately one-third (31.1%) reported having had receptive anal sex. In nearly three-quarters of these exchanges (71.4%), no condom was used. Similarly, in their last sexual encounter with a client partner, 42.2% reported having had insertive anal sex and in nearly half (47.4%) of these encounters no condom was used. Consistent with recent data from elsewhere in the region, there is an urgent need for additional research on male sex work in South-east Asia in order to properly situate behavioural interventions for male sex workers in this region.