The objective of the study was to establish a behavioural surveillance system (BSS) for sexually-related risk behaviours of the Hong Kong adult male general population. Benchmark data were obtained by interviewing 1,020 male respondents, age 18 to 60. The results showed that: (1) 14% of the respondents had engaged in commercial sex in the past six months, (2) 27% of the male commercial sex clients did not always use condoms when having sexual intercourse with commercial sex workers (CSWs), (3) 1.5% of the respondents had contracted sexually transmitted diseases (STDs) in the past six months, (4) 6.1% of respondents had only ever had sex with a man, (5) 0.8% of the respondents had practised unprotected anal intercourse with a man in a six-month period, (6) 4.4% of respondents practised sexually-related high risk behaviours, defined as unprotected sex with a CSW or unprotected anal intercourse with a man, and (7) 36.4% of those who engaged in commercial sex had not used condoms with their regular sex partners. Commercial sex was often practised outside Hong Kong, very commonly in Mainland China or Macau, and was often practised at multiple locations by the same client. Effective programmes have to be able to reduce the size of the at-risk population. This study together with future ones, will form the first BSS in Hong Kong for the general male population and will provide a relevant yardstick for programme evaluation.