The authors administered the Structured Clinical Interview for DSM-III-R to 260 patients with principal diagnoses of depressive disorders. Approximately two-thirds of these patients were given at least one additional concurrent axis I disorder. The most common comorbid diagnoses were anxiety disorders. The depressive disorders preceded the anxiety disorders in most patients. The authors not only point out the scientific and clinical implications of psychiatric comorbidity in view of the patterns of comorbidity found in this and previous studies but also discuss issues in comorbidity research.