Objective: Research studies on the validity of current diagnostic and subthreshold cate- gories of depression that use a population-based follow-up design are rare. The authors examined the validity and utility of four current depression categories by examining subject transition between categories and the symptoms, course, and risk factors of each. Method: A general population sample of 1,920 adults from the Baltimore Epidemiologic Catchment Area 13-year follow-up study were examined. Data on diagnoses, symptoms, course, and risk factors were collected by using the National Institute of Mental Health Di- agnostic Interview Schedule, the Life Chart Interview, and an office visit. Polychotomous regression was used to examine the heterogeneity of four diagnostic categories: major de- pressive disorder, depressive syndrome, dysthymia, and a comorbid depression condition (major depressive disorder and dysthymia). Results: Transitions between the four depres- sion categories occurred over the 13 years. Symptom profiles for the four categories were parallel but differed in severity. Course characteristics among the four categories slightly differed. Risk factor profiles showed significant differences. Family history was associated with both depressive syndrome and major depressive disorder. Stressful life events were most strongly associated with depressive syndrome. Female gender was most strongly as- sociated with the comorbid depression category. Conclusions: The evidence suggests that except for dysthymia, the depression categories are genetically homogeneous and en- vironmentally heterogeneous. Stress is associated with mild depression, and gender is as- sociated with severe depression. The apparent familial transmission of the subthreshold entity, depressive syndrome, needs further investigation. (Am J Psychiatry 2000; 157:573-580)