The psychiatric manifestations of Huntington's Disease (HD) include dementia, irritability and apathy, a major affective syndrome, and hallucinosis. The theoretical and practical utility of chorea as a focus of research interest in HD is questioned, whereas the data reviewed suggest that assessments of cognition, functional capacity and motor impairment are better correlated neuropathologically, and are better indicators of disease severity and progress than chorea. The high incidence of major affective disorders on modified DSM III criteria among HD patients (41 per cent) may be explained either as a manifestation of genetic heterogeneity within the HD phenotype or on the basis of genetic linkage between HD and manic depressive illness (MDI). This is supported by the high coincidence of HD and MDI (20 out of 23) among secondary cases of HD ascertained through probands having both disorders, indicating a strong familial clustering of the association. This implies that a young adult at risk for HD who has had episodes of severe depression has considerably more than 50 per cent likelihood of progressing to manifest HD. Although auditory hallucinations appear occasionally in patients with HD, most do not meet current criteria for schizophrenia.