OBJECTIVE: To estimate HIV prevalence and risks in university students. DESIGN: Anonymous self-completion questionnaire and HIV survey with saliva samples. SETTING: University students at matriculation. PARTICIPANTS: All first and third year undergraduates and newly registering postgraduates at the University of Edinburgh, Scotland. MAIN OUTCOME MEASURES: HIV prevalence, sexual behaviour, condom use, drug use. RESULTS: The questionnaire responses were used to classify the 4665 respondents into four groups, ordered by risk of HIV positivity, and a sample of 2041 was selected for testing. All of the top two risk groups were tested (217 and 758 tests, respectively) as well as a random sample of the others. Five positive HIV-antibody tests were detected, all from the highest risk group. This gives an estimated rate of 1.2 per 1000 (95% confidence interval, 0.4-2.9) for all respondents. Only one of the five HIV-positives had been tested for HIV. The factors associated with HIV positivity were residence in Africa, intravenous drug use and male homosexuality. Overall, 74% of respondents reported ever having had sexual intercourse and this rate was the same for men and women. Reported intravenous drug use was very low: 0.5% for men and 0.1% for women. Condom use was more common for partners of short acquaintance, but unrelated to the number of sexual partners in the last year. CONCLUSIONS: There was no evidence of the spread of HIV infection beyond known high-risk groups in this population. This may be a result of relatively low levels of HIV risk-taking behaviour in the majority of respondents.