OBJECTIVES: To assess sexual risk behaviour and prevalence of treatable sexually transmitted infections (STI) in migrant male workers in Lahore, Pakistan. METHODS: Behavioural interviews were conducted on a representative sample of 590 migrant men aged 20-49 years. Biological samples were collected from a subsample of 190 and tested for chlamydia, gonorrhoea, and syphilis. RESULTS: Over half (55%) of single men were sexually experienced and 36% of married men reported premarital sex. The median ages at first intercourse and first marriage were 21 years and 28 years, respectively. In the total sample (including virgins), 13% reported any female non-marital partner in the past 12 months, 7% contact with a female sex worker, and 2% sex with a man. Only 10% reported using a condom during most recent contact with a sex worker. STI symptoms in the past 3 months were reported by 8% of men. Laboratory tests disclosed that STI prevalence was 3.2%. CONCLUSIONS: If and when HIV infection spreads among sex workers in Lahore, the reported behaviour of migrant men suggests that they may act as a conduit for further transmission to the general population. Condom promotion focused on the sex trade is likely to be the most effective way of reducing this risk.