The objective was to assess levels of high-risk sexual behaviour, condom use, sexually transmitted disease (STD) history and AIDS-related perceptions among Hong Kong men returning from China by land; 1,254 systematically sampled subjects were interviewed. Of respondents, 32.5% had sexual intercourse with a commercial sex worker (CSW) in China in the past six months; 11.2% have done so on this trip. A third of those who reported having sex with CSWs did so without a condom. A fifth had a history of STDs: seventy per cent of respondents who did not use a condom with a CSW would not use a condom with their regular sexual partner. Less educated respondents, 31-40-year-olds and non-business and frequent travellers were more likely to have sex with a CSW. Those who practice high-risk sex fear AIDS more, are aware that their own risk of HIV infection is not negligible, but think that chances of HIV infection from CSWs in China are small. Although Hong Kong's estimated HIV prevalence among adults is low (0.06%), the huge volume of cross-border travel between Hong Kong and China and the common practice of high-risk sex by Hong Kong male travellers provide a bridge for emerging epidemics to spread.