Introduction: Adolescence can be defined as the period within the lifespan when most of a person’s biological, cognitive, psychological, and social characteristics are changing from what is typically considered childlike to what is considered adult-like. For the adolescent, this period is a dramatic challenge, one requiring adjustment to changes in the self, in the family and in the peer group. Emerging sexuality that accompanies adolescence poses fundamental challenges for young people. These include adjusting to altered appearance and functioning of a sexually maturing body, learning to deal with sexual desires, confronting sexual attitudes and values, experimenting with sexual behaviors, and integrating these feelings, attitudes, and experiences into a developing sense of self. So both sexual ideation and activity increase over the adolescent period. Teenagers engage in a spectrum of sexual behaviors ranging from fantasy and self stimulation to various forms of intercourse. On the other hand, the risk of acquiring a sexually transmitted disease and adolescence pregnancy with sexual behaviors is increasing. For developing effective interventions to reduce risky sexual behaviors, it is critical to describe to prevalence of sexual behaviors among adolescence and identify risk and protective factors. The purpose of this study were to determine the frequency of precocious sexual intercourse behavior, evaluated sexual intercourse behavior according to gender variable and investigated the role of psychosocial factors in adolescent precocious sexual intercourse behavior among 15-17 ages adolescents. Materials and Methods: A total of 1774 high school students, in Izmir participated in this study. Students completed Adolescent Health and Development Questionnaire (AHDQ). AHDQ designed to test the usefulness of Problem Behavior Theory. Problem Behavior Theory which is developed Jessor and Jessor (1977) describes the relationship of protective and risk factors, which is including not only individual factors but also multiple social factors, to involvement in problem behaviors such as smoking, alcohol use, marijuana and other illicit drug use and early sexual intercourse experience. Frequency analysis, Chi-square test, Pearson Correlation Analysis and, hiererchical regression analysis were used to data regarding the sample. Results: 22% of the adolescents were being sexual intercouse participants stated that 43% of them unprotected while being first sexual intercourse and 19% of them being pregnancy of themselves or partners. Boys were being sexual intercourse more than girls and they had more partners than girls. At the same time boys were use less protective methods than girls. Also the most common protective methods are coitus interruptus and condom use. And precocious sexual intercourse behavior are associated with positively increased rates of risk factors and also associated with negatively decreased rates of protective factors. At the same time psychosocial factors account for 33% of variance in precocuios sexual intercourse behavior. Conclusion: Precocious sexual intercourse may be cause to the some of the health and psychological problems. Prevention of precocious sexual intercourse among adolescents, adolescents' biopsycho-social development should be supported in the light of risk and protective factors.