Our objective was to describe HIV/STD risk behaviours and awareness among a community-based sample of drug users in Pakistan. Drug users contacted through street outreach by a non-governmental organization in Quetta, Peshawar and Rawalpindi underwent interviewer-administered questionnaires. Descriptive statistics were used to characterize sexual behaviours by city, marital status and the use of injection drugs. Logistic regression was used to identify correlates of ever having an STD. Of 608 drug users studied, all but one was male; median age was 32 years and 45% had no formal education. Half were married, of whom 25% were living with their wives. Sexual behaviours were reported as follows: 14% had sex with other males, 28% reported sex with both males and females, 49% had paid money to have sex and only 10% had ever used condoms. One-fifth reported having had an STD and about 40% reported having suffered from either one or more STD-related symptoms. Only 41% had heard about HIV/AIDS, of whom 17% knew that HIV/AIDS could be transmitted through sexual contact. In conclusion, high-risk sexual behaviours are prevalent among male drug users in Pakistan, and awareness of transmission risks is low. These data attest to the urgent need for effective and specific interventions in Pakistan to prevent transmission of HIV and STDs among drug users and their sex partners.