Research indicates that bulimia is a fairly common disease among adolescent girls. However, the longitudinal processes involved in predicting the development of bulimia are not yet well understood. This study therefore examined the role of parents, peers, and the individual in predicting bulimic symptoms during the transition to adolescence. Specifically, we hypothesized that sociocultural parent and peer factors (e.g., direct encouragement to lose weight or pressure to be thin and discussions about dieting) would lead to individual body dissatisfaction and dieting behaviors among adolescent girls. Body dissatisfaction would then lead to dieting behaviors and depressive symptoms, which in turn would predict the development of bulimic symptoms. Four years of self-report data were collected from 87 adolescent girls during 5th through 8th grades. In model testing, parent and peer influences were first examined separately and then together in combined models, in order to determine whether parents or peers more strongly contributed to the development of adolescent girls’ bulimic symptoms. When considered separately, mothers, fathers, and peers drove the process leading to adolescent girls’ bulimic symptoms. When parents and peers were considered together, peers appeared to be a stronger contributor to the development of body dissatisfaction while both parents remained important influences on dieting behaviors; these attitudes and behaviors ultimately led to bulimic symptoms. In examining models with maternal and paternal influences together, fathers’ contributions appeared to be stronger than mothers’. These results indicate that both parents and peers are important influences in the process leading to adolescent girls’ bulimic symptoms. In particular, future prevention and intervention work with girls during the transition to adolescence should target both parents and peers, with a particular emphasis on involving fathers and peers.