Using the National Youth Survey (NYS), the Sexual Assault Project (SAP) completed interviews with 172 female victims from 1978 through 1980 and 68 interviews with male offenders. These data showed that between 5 to 11 percent of the adolescent female population experienced at least one sexual assault, but revealed no significant race or social class differences or consistent age trends. However, vulnerability to sexual assault increased sharply after an individual became a victim. For most victims, the assault occurred in their homes, the offender's home, or a car, and the offenders were primarily boyfriends or dates. Over half the victims reported verbal pressure, while 27 percent to 40 percent mentioned some minimal physical force. Most victims offered verbal and/or physical resistance and were successful in deterring the assault. The strongest initial reactions to assault were anger, depression, and embarrassment, with some 40 percent also reporting guilt. These reactions were not differentiated by demographic variables, but victims who successfully deterred the attack reported substantially fewer negative reactions than those who were assaulted. Followup data 2 to 3 years after the attack suggested that reactions may intensify with time, such as depression and fear of being alone. While the study's findings did not support the typical image of assault victims as black, lower class urban females, they did indicate that engaging in delinquent behavior and being part of a delinquent network influenced the risk of being sexually assaulted. Offenders' reactions to sexual assault were ambiguous, but reactions from friends were almost completely approving. Additional study results are noted. Tables, additional materials on the survey's methodology including the interview questionnaire, over 100 references, and an index are supplied.