Data on the prevalences, comorbidities, and cohort effects of DSM-III-R major depression (MD) and minor depression (mD) are reported for the nationally representative sample of n = 1,769 adolescents and young adults who participated in the National Comorbidity Survey. Lifetime prevalences are 15.3% (MD) and 9.9% (mD), while 30-day prevalences are 5.8% (MD) and 2.1% (mD). Most cases reported recurrent episodes (73.9% of those with MD and 69.2% with mD) and significant role impairment, including attempted suicide among 21.9% of those with MD. The majority of lifetime cases (76.7% of those with MD and 69.3% with mD) reported other comorbid lifetime NCS/ DSM-III-R disorders. Depression was temporally secondary in the majority of these cases. Number of prior disorders was more important than type of disorders in predicting subsequent depression, raising the possibility that secondary depression is a nonspecific severity marker for earlier disorders. A cohort effect for both MD and mD was documented that persisted even for episodes lasting a year or longer. Increasing prevalences of prior comorbid disorders were found to play an important part in explaining the cohort effect for depression.