OBJECTIVES: The aim of this study was to assess the relationship between background and sociodemographic variables, attitudes toward controversial aspects of human sexuality and sex knowledge among medical and nursing students. METHOD: The study design was a questionnaire-based survey of medical and nursing students in Western Australia. Participants were first- through fifth-year medical students at the University of Western Australia and first- through third-year undergraduate nursing students at Edith Cowan University. Outcome measures were students' attitudes toward controversial aspects of human sexuality expressed on a five-point Likert scale and a modified version of the Kinsey Institute/Roper Organization National Sex Knowledge Test. RESULTS: A significant relationship was found between certain background and sociodemographic variables, sexual attitudes and sex knowledge. The background variable most strongly related to both attitudes and knowledge was frequency of attendance at religious services of any religious denomination during the past month, with those attending three or more times more likely to express negative attitudes and have lower sex knowledge scores. Lower sex knowledge was related to negative attitudes toward gay/lesbian/bisexual behaviour, masturbation, premarital sex and contraception. Other important background and sociodemographic variables related to negative attitudes were: never having experienced sexual intercourse; right-wing political orientation; lower family income; gender and ethnicity. CONCLUSIONS: Negative attitudes toward controversial aspects of human sexuality and lower sex knowledge scores among medical and nursing students can be predicted on the basis of background and sociodemographic variables. Education aimed at increasing sex knowledge and modifying negative attitudes may increase students' ability to function more effectively as sexual history takers and sex counsellors.