To examine adolescent depression as a model for unusual emotion regulation, the current study considered the influence of gender, pubertal development, and cortisol on self-reported mood. Children and adolescents with major depressive disorder (n = 35, mean age 12.5 years) were compared with psychiatrically healthy children and adolescents (n = 36, mean age 10.5 years). During a three-day assessment, participants rated their mood at three time points, pubertal development was determined through physical examination, and plasma cortisol was sampled during the second night. Depressed participants experienced less positive affect and more negative affect than did controls. Diagnostic group, gender, and pubertal status interacted to predict negative affect, with depressed adolescent girls experiencing especially high levels of negative affect. Cortisol was generally unrelated to depression and mood. Findings are consistent with emotion-based models of depression and with the literature on depression and emotion regulation during adolescence.