This study assessed the hypothesis that popularity in adolescence takes on a twofold role, both marking high levels of concurrent psychosocial adaptation, but also predicting increases over time in both positive and negative behaviors sanctioned by peer norms. This hypothesis was tested with multi-method, longitudinal data obtained on a diverse community sample of 185 adolescents. Sociometric popularity data were examined in relation to data from interview-based assessments of attachment security and ego development, observations of mother-adolescent interactions, and repeated self- and peer-report assessments of delinquency and alcohol use. Results indicated that popular adolescents displayed higher concurrent levels of ego development, secure attachment and more adaptive interactions with mothers and best friends. Longitudinal analyses supported a “popularity-socialization” hypothesis, however, in which popular adolescents were more likely to increase in behaviors that receive approval in the peer group (e.g., minor levels of drug use and delinquency) and decrease in behaviors unlikely to be well-received by peers (e.g., hostile behavior with peers).