This report on sexual assault was written for adults who work with adolescents. It contains data on teenage sexual assault from the National Youth Survey (NYS), a survey of a nationally representative sample of approximately 1,700 youths who were between 11 and 17 years old at the time of the project's initial interview and who were interviewed annually for 5 years (1976-1980). The data in this report came from the final 3 years of the NYS when detailed information about sexual assaults was obtained from all the self-identified victims and offenders. The research project is briefly described, the study results are presented, and implications of the findings for counseling adolescents about the risk and effects of sexual assault are discussed. The frequency of sexual assault among teenagers and the proportion of teenagers affected are presented, and the typical adolescent assault is described. A section on the aftermath of a sexual assault considers reporting the assault to the police, personal relationships, and personal behavior and reactions. A section on the risk of sexual assault includes a comparison of victims and nonvictims and concludes that the risk is greater for teenagers who engage in delinquent activities with their friends, although teenagers who engage in delinquent activities are not the only victims of sexual assault. The final section, "Reducing the Risk of Sexual Assault among Teenagers," outlines four steps to avoid sexual assault and summarizes advice to teenagers. (NB)