Adolescence is considered as an important phase for beginning sexual high risk behaviors that increases the possibility of negative, unpleasant and problematic consequences like unwanted pregnancy and probability of copulative disease transmission.To determine the prevalence of sexual risk taking among students in Tehran and to develop and test a model for the relationship between parental monitoring and affiliation with deviant peers as they predict youth risky sexual behaviors.In this cross sectional study, 1266 adolescents were recruited from high schools in Tehran and three scales of sexual risk behavior, parental monitoring and adolescent affiliation with deviant peers were completed. Data was analyzed using independent sample t-test, Pearson correlation coefficient and structural equation modeling.According to the results, about one-fifth of subjects were at high risk in terms of unsafe sexual relationships. The percent of positive attitude among males was nearly 2 times more than that of females. The investigated model for the mediating role of affiliation with deviant peers in the relationship between parental monitoring and sexual risk taking was confirmed and explained 0.32 of sexual risk taking variance.The results of this study suggested that parental monitoring and affiliation with deviant peers largely explained sexual risk taking among adolescents. Therefore, prevention efforts aimed at reducing risky sex should compose of these factors. In fact, the results suggested that earlier prevention efforts may be warranted.