Few studies have described levels and determinants of perceived risk of HIV-1 among African adults for whom the sero-status is known. This study describes HIV risk perception obtained from a large rural population in south-west Uganda which also underwent serological testing for HIV. Cross-sectional survey. Information on risk perception and sexual behaviour was collected by interview. Sera were obtained from all consenting adults (13 years and above) in order to assess HIV-1 prevalence. Of 14,818 adults with a definitive sero-status, 9.7% were HIV-1 positive and 51% considered themselves to be at risk of infection. Risk perception showed similar patterns as age- and sex-specific sero-prevalence and there was correspondence between risk factors for perceived risk and known HIV risk factors. Partner's sexual behaviour was the commonest reason for risk perception in women whereas men cited their own sexual behaviour. Abstinence from sex was much more commonly mentioned as a protective practice than condom use in men and women. Half of the adults we have studied already see infection with HIV as a real possibility in their lives and are aware of HIV risk behaviours. More efforts should be made to implement sustainable control measures rather than simply raising awareness. In addition to recommending abstinence, these include mutual faithfulness, condom use and better treatment for STDs.