OBJECTIVE To describe adolescent knowledge, attitudes and behavior relevant to sexuality and the prevention of AIDS in Saint Petersburg, Russia. METHODS A cross-sectional descriptive study was designed, taking a random sample of 10th grade students at 14 Saint Petersburg grade schools, which were stratified by socio-economic district. A total of 185 female and 185 male students completed a self-administered 46-item questionnaire, with a response rate of 94%. RESULTS From the questionnaires, 20% of females and 31% of males reported having had sexual intercourse and 25% of females and 12% of males reported being sexually abused. These adolescents displayed much misinformation about sexual matters and AIDS prevention. Only 25% of the females and 34% of the males believed that condoms should be used just once, and 38% of each sex believed that if washed, they could be used multiple times. Many respondents, especially males, rated their knowledge about sexual matters as high or adequate. Support for sex education was strong, especially among females, and respondents generally saw sex education as improving sexual pleasure. Most information sources about sexual activity were either not considered very credible, or not adequately accessible. CONCLUSIONS Substantial reported rates of sexual abuse, sexual experience and much misinformation and unwarranted attitudes toward condoms, safer sexual practices and HIV/AIDS suggest the need for vigorous sex education programs for Russian youth. The early and sustained education of girls is especially important. Sex education should be introduced at an early age so that children can be taught how to reduce the risks of sexual abuse, HIV infection and other sexually transmitted diseases, and to improve their sexual experiences as responsible adults.