Several measures of family configuration, derived from the number, age, and sex of siblings and the number of parents, were related to adolescent sexual attitudes and behavior in a sample of 836 high school-aged teenagers from two Western states. Zero-order correlations showed that sexual intercourseexperience was less common among adolescents who lived with both parents and also among those who had younger siblings. Similarly, the zero-order correlations showed least permissiveattitudes among adolescents who had more siblings, especially younger siblings, and among those who lived with both parents. Controlling for adolescents' age, sex, race, religion, church attendance, and parents' educational attainment, however, essentially eliminated the relationships between family configuration variables and sexual attitudes and behavior. Only parents' marital structure, reflecting whether adolescents lived with both original parents or not, continued to be weakly related to adolescents' sexual attitudes and behvior.