In 12 patients with Huntington's disease, the relationship between brain morphology, nocturnal sleep EEG, and clinical variables was studied. Global cerebral atrophy did not significantly correlate with sleep parameters, whereas atrophy of the caudate nuclei was associated with reduced slow wave sleep and increased time spent awake. Several clinical parameters (e.g., anergia and thought disturbance scores of the Brief Psychiatric Rating Scale, illness duration and global clinical assessment) showed significant correlations with global cerebral atrophy. Similar studies in other neuropsychiatric disorders demonstrate associations between sleep alterations and brain morphological changes of different localizations, thus pointing to a complex relationship between both. It can be hypothesized that the caudate nuclei may be involved in sleep regulation; indirect evidence from studies with positron emission tomography (PET) point in the same direction.