This paper challenges the traditional conceptualization of depression as a primary mood disorder. Clinical and biological research findings support the hypothesis that 'depression' in old age is a final common pathway of central nervous system dysregulation. This accounts for the varied clinical presentations, cognitive changes and diverse neurobiological abnormalities found in the depressed elderly. Clarification of the concept of depression in old age will help to improve clinical management and have heuristic value in developing better research strategies.