The current research examined co-rumination (extensively discussing, rehashing, and speculating about problems) with mothers and friends. Of interest was exploring whether adolescents who co-ruminate with mothers were especially likely to co-ruminate with friends as well as the interplay among co-rumination with mothers, co-rumination with friends, and anxious/depressed symptoms. Early- to mid-adolescents (N = 393) reported on co-rumination and normative self-disclosure with mothers and friends and on their internalizing symptoms in this cross-sectional study. Co-rumination with mothers (but not normative self-disclosure) was concurrently associated with adolescents' co-rumination with friends. In addition, the relation between co-rumination with mothers and adolescents' anxious/depressed symptoms reported previously (Waller & Rose, 2010) became non-significant when co-rumination with friends was statistically controlled. This suggests that the relation between friendship co-rumination and anxious/depressed symptoms may help explain the relation between mother-child co-rumination and anxious/depressed symptoms. Potential implications for promoting adolescents' well-being are discussed. (Contains 2 tables and 1 figure.)