This study assessed the stability of adolescents' social networks over a school year, focusing on the stability of close friendships, best friendships, friendship groups, and the adolescent's role in his or her social network. As part of an ongoing Adolescent Peer Influence Project, 6th-, 8th-, and 10th-grade students from a working class suburban school district were followed longitudinally over an academic year. Approximately half of the students participating in this study were females; 75 percent were African-American. Students were asked to name a best friend and up to nine friends in the fall and again in the spring of the same academic year. Analysis revealed that all levels of adolescents' friendship networks in this study showed moderate stability, but that overall, girls' friendship networks were more stable. Stability of close friendships and cliques increased with grade level. However, stability of best friendships did not differ by grade. Reciprocal friendships were more stable, and stability of friendship networks were either weakly correlated or uncorrelated with self-report and teacher-report measures of delinquency and scholastic competence. (MM)