OBJECTIVES To review and summarise various types of Peruvian evidence on sexual behaviour, HIV/STI exposure and risk, and discuss how to increase its usefulness for HIV/STI risk trend monitoring in Peru. METHODS Review HIV sentinel surveillance conducted by the Ministry of Health; data from the Demographic and Health Surveys (DHS); and academic publications on sexual behaviour in combination with biological markers. Changes over time, quality of data, size of studies, and intended audience are discussed. RESULTS Data from HIV sentinel surveillance showed very high (8-23%) HIV seroprevalence among men having sex with men, but stable, relatively low figures among female sex workers (1%) and antenatal clinic patients (under 0.5%). DHS data suggest that single women increased their sexual activity throughout the 1990s but did not raise their contraceptive use accordingly, resulting in increased early conceptions. The contribution of condoms to overall contraceptive protection increased threefold in 1992-2000. According to the 1996 survey, men become sexually active 2.5 years earlier than women, but marry or cohabit four years later than women; women marry or cohabit 1.5-2.5 years after first sex, whereas men take eight years to do so. Finally, published studies confirmed dramatic differences in HIV prevalence between men who have sex with men and other populations, and also suggested patterns of bridging from men to women. CONCLUSIONS Data available from the three sources are numerous, although limitations of each approach reduce their monitoring utility: Ministry of Health studies should select better sentinel populations and timely process behavioural data. Future demographic surveys should incorporate an AIDS risk perspective and include men.