This study will fill an important gap in AIDS research by describing predictors of HIV risk behavior in an ethnically mixed sample of young adolescents living in an AIDS epicenter. The study will identify precursors of entry into dysfunctional peer groups (crowds') and identify the substantive characteristics of crowds that promote risky activities (e.g., sexual behavior, drug use). These data will provide avenues for innovative school based interventions that address specific prevention needs of different crowds. Additionally, the study will yield methodological advancements in the measurement of adolescent social groups. The validity of a new method of assessing crowd affiliation will be tested in a cross-sectional study of 250 7th grade junior high students during year 1. The established method of assessing crowd membership (informant interviews) will be compared with with a new method using group administered questionnaires in randomly selected classrooms. If the new method proves valid, it will be used in place of the established method in the longitudinal segment of the study. A three year longitudinal study in two junior high schools (n=680) will begin in year 2. This study will: 1) identify the crowd structure for the 7th grade in two ethnically mixed junior high schools, 2) map changes in crowd structure, crowd membership, and crowd norms from 7th to 9th grade, and 3) examine the interrelationships of crowd affiliation and changes in crowd affiliation with domain specific self-concept, sexual behavior, and drug use over the course of junior high school. The longitudinal nature of the study will provide important data on social group development and crowd characteristics during early adolescence and on the impact of crowd affiliation on risky behavior.