1. Movement was monitored continuously for 24-48 hours in representative neuropsychiatric patients, using a wrist-worn portable piezoelectric activity monitor with solid-state memory. 2. Striking differences were observed in both circadian and more rapid (ultradian) rhythms between these patients and normal controls of a similar age. 3. We found a loss of circadian rhythm following stroke, and a marked 4-hour activity rhythm in patients with dementia and brain tumor. 4. These results may provide insights into the neural substrate of activity rhythms and may lead to better care of neuropsychiatric patients.