Thirty-one subjects affected by different movement disorders underwent polygraphic and videotape monitoring during nocturnal sleep, to assess movement patterns during the night. It was possible to distinguish two categories of disorders according to their pattern of movements. In the largest group (Meige's syndrome, blepharospasm, amyotrophic choreoacanthocytosis, Tourette syndrome, tonic foot, hemiballism) abnormal movements were still present during sleep, but decreased in frequency and amplitude in all stages. The second group presented three syndromes (nocturnal paroxysmal dystonia, nocturnal myoclonus, restless legs syndrome), in which light non-rapid-eye-movement sleep induced a strong activation of abnormal movements, whereas rapid-eye-movement sleep suppressed them.