In summer 1987, 584 students at Oxford University were sent a questionnaire enquiring about their sexual behaviour and contraceptive practice, and about the effect that AIDS has had on these. Of the 374 students who replied, 65% of the women and 62% of the men had experienced sexual intercourse. Twenty-seven per cent of female undergraduates did not use adequate contraception on the first occasion of intercourse. During the 4-week period preceding the questionnaire, 15% of sexually active female undergraduates did not use adequate contraception. The use of contraception has changed over the last 5 years, with fewer students using oral contraceptives as their most frequent means of contraception and more using barrier methods. In general, knowledge about AIDS was high. Most students did not consider that they were at risk of becoming infected by the AIDS virus and, by their reported sexual behaviour, very few students appeared to be at any risk. However, 35% of women and 44% of men who were sexually active said that because of risk of AIDS they had been more likely to use the sheath, and 49% of women and 30% of men said that they had, or would have, fewer partners. These findings suggest that attitudes, and possibly behaviour, are changing towards a reduction in risks of sexually transmitted infection.