Motor activity was quantitatively assessed over a period of 5 days using a wrist-worn activity monitor in 14 patients with Huntington's disease (of whom 4 used neuroleptic drugs) and 14 age and sex-matched healthy controls. Additionally, patients were rated for dementia, depression, clinical impairment of motor tasks, chorea, and disability. A significant decrease in daytime motor activity was observed in patients compared with controls, suggesting hypokinesia rather than hyperkinesia. Hypokinesia tended to be more severe in patients using neuroleptic drugs. Lower activity levels were significantly related to lower scores of functional disability, but not to other clinical measures. We conclude that hypokinesia is a prominent manifestation in Huntington's disease that is worsened by the use of neuroleptics.