The authors summarize current knowledge regarding the psychomotor symptoms of depression.Findings from the objective quantification of psychomotor symptoms are reviewed, and methodological issues are considered. The contemporary empirical literature regarding the diagnostic, prognostic, and potential pathophysiologic significance of psychomotor symptoms is summarized.It has been repeatedly shown that depressed patients differ from normal and psychiatric comparison groups with regard to objectively quantified gross motor activity, body movements, speech, and motor reaction time. Course of illness, diurnal variation, medication status, sex, and age are associated with agitation and retardation and should be controlled when one is studying psychomotor symptoms. Psychomotor symptoms in depression may have unique significance. They have high discriminative validity, may be the only symptoms of depression that distinguish depression subtypes, and are predictive of good response to tricyclic antidepressants. Results of brain imaging and biochemical studies link depression and motor symptoms to abnormalities in the basal ganglia and basal ganglia/thalamo-cortical circuits.The investigation of psychomotor disturbance in depression is specifically consistent with neo-Kraepelinian standards for the study of psychiatric disorders. Our current knowledge of psychomotor symptoms is conceptually obscure, yet a large body of evidence specifies their manifestation and supports their significance. Identifying the incidence of abnormal motor behaviors in depressed patients and assessing the component processes that accompany and determine their manifestation may be important advances in the study of psychomotor symptoms in depression.