The prospective relationship between initial rumination and subsequent bulimic symptoms, and vice versa, was examined, and possible mediators were tested in a community sample of 191 adolescent girls (M age = 14.5) at 3 different assessment time points. Path analyses indicated that Time 1 rumination predicted Time 3 bulimic symptoms, and vice versa. Physical appearance competence (but not social competence) mediated both relationships. The results suggest that specific cognitive mechanisms, such as rumination, may play an etiological role in the development of bulimic symptoms. This may be especially true for adolescent girls who exhibit low competence beliefs about their physical appearance. (Contains 1 table and 2 figures.)