Co-rumination, defined as repetitive, problem-focused talk explains higher levels of friendship quality in youth (Rose, 2002) and increased levels of anxiety/depression in females. Middle adolescents (N = 146) participated in a study of co-rumination, individual coping, externalizing/internalizing problems, and peer functioning. Consistent with past research, girls reported higher levels of co-rumination and internalizing symptoms. Co-rumination was also positively correlated with self-reports, but not teacher reports, of anxiety/depression and aggressive behavior. Both self-reported number of friends and teacher-rated social acceptance were negatively associated with co-rumination. Co-rumination partially accounted for the significant indirect effect of gender on internalizing symptoms. Additionally, co-rumination was associated with internalizing and externalizing symptoms but not individual coping efforts. Finally, co-rumination accounted for a unique amount of variance in internalizing symptoms, controlling for externalizing problems and secondary control coping. Theoretical implications and the importance of including broad domains of adjustment and peer functioning in future investigations of co-rumination are discussed. (Contains 3 tables and 1 figure.)