In this study, 31 patients with involutional-onset major depression had significantly more somatization and hypochondriasis and less loss of libido, guilt, suicidal intent, and family history of depression than 60 patients with an earlier onset. Regardless of age at onset, patients over age 50 had more agitation, initial insomnia, and hypochondriasis than those under 50. These findings suggest that clinical characteristics of patients with unipolar endogenous depression may be influenced by age at both onset and time of current episode. Although there is insufficient evidence to view involutional melancholia as a separate clinical entity, further research into the genetic and biochemical basis of late-onset depression is warranted.