Co-rumination predicts the onset of depressive disorders during adolescence.

The tendency to co-ruminate, or frequently discuss and rehash problems with peers, may serve as one mechanism in the dramatic rise in depression observed during adolescence, particularly among adolescent girls. In the current study, our goal was (a) to test the hypothesis that adolescents' levels of co-rumination would predict the onset of clinically significant depressive episodes over a 2-year follow-up and (b) to determine whether levels of co-rumination would mediate gender differences in risk for depression onset. Both hypotheses were supported. Results of survival analysis revealed that adolescents with higher levels of co-rumination at the initial assessments exhibited a significantly shorter time to depression onset. Levels of co-rumination also mediated the gender difference in time to depression onset. These results were maintained even when adolescents' baseline levels of depressive symptoms and rumination were covaried statistically. Finally, co-rumination also predicted the course of illness in terms of episode severity and duration. Results suggest that co-rumination contributes a unique risk for the development of depression in adolescents.