Recent data indicate that adolescent fertility rates in Peru remain high and that Peruvian adolescents and young adults account for a disproportionate share of new HIV infections. The present study was undertaken to identify key risk and protective factors for early sexual activity and unprotected sex among secondary-school students in nine large cities in Peru. Survey data from 6,962 students aged 13-18 are consistent with existing research in indicating that behaviors of Peruvian youth are influenced in important ways by many factors. In the present study, these included region of residence, family economic position, family structure, working for pay, peer behaviors, and self-esteem. Knowledge of pregnancy and of the risks of acquiring sexually transmitted diseases and of the means of avoiding both did not, however, differentiate risk-takers from non-risk-takers. The study findings suggest a need for adolescent health programs to broaden their focus beyond the immediate proximate determinants of behavior, such as sexual and reproductive health knowledge and access to contraceptives, and also to target some of the key contextual factors influencing adolescent behavior.