This multiwave longitudinal study investigated potential transactional and accumulating influences among corumination, interpersonal stressors, and internalizing symptoms among a sample of early and middle adolescents (N = 350; 6th–10th graders). Youth completed self-report measures of corumination at Times 1, 2, and 4, and negative life events, internalizing symptoms (general depressive, specific anhedonic depressive, anxious arousal, general internalizing), and externalizing problems at all four time points (5 weeks between each assessment across 4 months). Results supported hypotheses. First, baseline corumination predicted prospective trajectories of all forms of internalizing symptoms but not externalizing problems. Second, baseline corumination predicted generation of interpersonal-dependent, but not interpersonal-independent or noninterpersonal stressors. Third, interpersonal-dependent events partially mediated the longitudinal association between baseline corumination and prospective internalizing symptoms. Fourth, a transactional, bidirectional set of associations was supported in that initial internalizing symptoms and stressors predicted later elevations in corumination, and in turn, corumination predicted later symptoms through the mediating role of interpersonal stressors to complete both streams in the transactional chain of influence. Fifth, girls and older adolescents exhibited higher corumination, but neither age nor sex moderated any associations. These findings are discussed within a transactional, developmental cascade model.