Reports on three patients (46-yr-old man, 19-yr-old woman, and 13-yr-old boy) with sleepwalking associated with severe hyperthyroidism. Their sleepwalkings were reversed with antithyroid therapy. The authors argue for the presence of symptomatic subgroup of treatable sleepwalkers with hyperthyroidism characterized by the lack of past history of sleepwalking, night terrors or other parasomnia, and by the absence of a family history of sleepwalking.