Rett's syndrome is a progressive disorder that occurs in females and is characterized by autistic behavior, dementia, ataxia, loss of purposeful use of the hands, and seizures. Patients with Rett's syndrome have been observed to have stereotyped hand movements (hand-washing) and to exhibit intermittent hyperventilation. To characterize more precisely the sleep and respiratory patterns associated with this disorder, polygraphic studies were made during sleep and wakefulness in 11 patients with this syndrome. These studies showed abnormal respiratory patterns during wakefulness, and abnormal sleep and electroencephalographic characteristics. The patients had decreased percentages of rapid-eye-movement sleep, and during wakefulness, a pattern of disorganized breathing was observed in all 11 patients and consisted of hypoxia followed by a period of increased respiratory rate and effort. The occurrence of disorganized breathing and compensatory hyperpnea during wakefulness with regular, continuous breathing during sleep is characteristic of Rett's syndrome and suggests an altered or impaired voluntary/behavioral respiratory control system.