Thirty patients with Huntington's disease, a genetically transmitted neuropsychiatric disorder that can be diagnosed reliably, were evaluated systematically for psychopathology, followed for extended periods, and treated with psychopharmacological medications when necessary. DSM-III criteria were used for establishing syndromic diagnoses. Twenty-four individuals demonstrated substantial behavioral abnormalities, including affective and schizophrenic syndromes, changes of personality, and disorders that could not be classified adequately. Pharmacotherapy was modestly beneficial in some cases. Consideration of the array of behavioral disturbances encountered in this pathogenetically unified disorder suggests that a dimensional approach to symptom classification might prove more useful heuristically than present typological methods.