To describe attitudes towards HIV infection in relation to sexual risk behaviour and sociodemographic factors in a representative sample of Danish men 16-55 years of age, a self-administered anonymous questionnaire was distributed in connection with a personal health interview and returned by prepaid mail. The response rate was 55%, corresponding to 1,155 participants. In contrast to the official AIDS prevention strategy, 28% of the participants stated that HIV infected persons should be forbidden to have sexual relationships, and 44% that they should be registered by the authorities. 33% of the participants had had sexual behaviour which may be associated with increased risk of HIV infection: More than one female partner during the previous 12 months, sexual contact with prostitutes or sex with other men. Despite good basic knowledge of AIDS, only 41-59% of these men perceived themselves at risk, and only 47-54% of men perceiving themselves at risk had adopted risk-reducing sexual behaviour. The results indicate a need for innovative health education of the general public about AIDS prevention at community and individual level. In the absence of effective treatment and without prospect of a vaccine in the near future the prevention of AIDS must focus on modifying behaviour associated with increased risk of HIV infection, in particular sexual behaviour.