In Pakistan, male sex workers are predominantly transvestites and transsexuals known as Hijras. In 1998 in Karachi, Pakistan, we studied the seroprevalence of HIV, HBsAg and syphilis and associated risk factors in Hijras. Study subjects were verbally administered a structured questionnaire that determined risk behaviours for sexually transmitted and blood-borne diseases and knowledge of AIDS/STDs. After pre-test counselling, verbal consent was taken for serological testing. The results were provided on a one-on-one post-test counselling session. Three hundred male transvestites were approached; all agreed to answer the questionnaire, 208 consented to blood testing. Of 300, 81% acknowledged commercial sex with men. Of 208, prevalence of syphilis was 37%; HBsAg 3.4%; HIV 0%. The prevalence of HIV and hepatitis B virus (HBV) is low in transvestite sex workers but that of syphilis is high. Intervention programmes implemented at this stage can have an impact on HIV and STD prevention.