Variability in adolescent-friend similarity is documented in a diverse sample of African American, Asian American, and European American adolescents. Similarity was greatest for substance use, modest for academic orientations, and tow for ethnic identity. Compared with Asian American and European American adolescents, African American adolescents chose friends who were less similar with respect to academic orientation or substance use but more similar with respect to ethnic identity. For all three ethnic groups, personal endorsement of the dimension in question and selection of cross-ethnic-group friends heightened similarity. Similarity was a relative rather than an absolute selection criterion: Adolescents did not choose friends with identical orientations. These findings call for a comprehensive theory of friendship selection sensitive to diversity in adolescents' experiences. Implications for peer influence and self-development are discussed.H. S. Sullivan's (1953) seminal theorizing on the developmental features of friendship calls attention to the importance of shared interests, attitudes, and behaviors between adolescent friends in meeting basic social needs of companionship and intimacy. Close friendships are thought to be the most rewarding when both partners pursue activities and interests that are mutually engaging. Intimate self-disclosure, critical to adolescents as they come to understand who they are and what their place is in the world, is most satisfying and beneficial when it occurs between peers who share similar views with respect to issues of fundamental importance to them (Youniss & Smollar, 1985). Social psychological theory and research findings, too, demonstrate that similarity is a key platform for friendship selection and emphasize that adolescents seek friends who share endorsement of activities and orientations that are of consequence to them (T. M Newcomb, 1961; This study was completed in partial fulfillment of the requirements for the Master of Science degree at the University of Wisconsin-Madison.