The role of peer acceptance, number of mutual friends, and friendship quality in predicting adjustment across the transition from elementary to middle school was examined. Participants were 146 students (68 boys, 78 girls) who participated in the Time 1 (spring of fifth grade) and Time 2 (fall of sixth grade) assessments. Peer acceptance and number of friends were assessed using sociometric rating scale and limited nomination procedures. Participants also completed measures that assessed feelings of loneliness, extent of involvement in school, and the quality of a specific mutual friendship. Results of repeated measures MANOVAs revealed a significant decrease in the average number of mutual friendships across time. Regression analyses indicated that peer acceptance and friendship quality and quantity play significant yet somewhat different roles in predicting loneliness and school involvement across the middle school transition. Implications for including a peer component in programs that prepare students for the middle school transition are discussed. (Contains 4 tables.)