Sleep rhythm can be influenced by narcotics and exogenous disturbances causing persistent insomnia, exhaustion and moodiness. In this study the influence of anesthesia on the patients’ sleep during the first postoperative night was investigated. It was attempted to differentiate between the influences due to anesthesia, namely to surgery, and due to intensive care. In 10 patients with halothane narcosis, 12 patients with neuroleptanalgesia, 12 young patients and 12 patients more than 70 years of age with halothane/fentanyl anesthesia a sleep study was performed during the first postoperative night. Electrodes were placed according to the criteria of Rechtschaffen and Kales [US Department of Health, Education and Welfare, Public Health Service, Bethesda 1968]. The group of controls consisted of 10 healthy female volunteers, who had to sleep under identical conditions. The sleep stages were visually evaluated by criteria of Rechtschaffen and Kales [US Department of Health, Education and Welfare Public Health Service, Bethesda 1968]. The disturbances by nurses did not, on the whole, interfere with the sleep rhythms of the 10 healthy volunteers: 4–5 REM phases and stage IV sleep were seen regularly. The patients had a maximum of 1 REM phase. Stage II sleep was reached after falling asleep and maintained for several hours. Stage III and IV were hardly seen in all patient groups. Geriatric patients showed the most obvious changes in their sleep. They were sleepless during 41.1 % of the monitored period. Stage II was slightly reduced. Night sleep of patients after anesthesia is disturbed not only by intensive care unit conditions, but also by direct effects of narcotics and surgery. Disturbances of the night rest can cause severe confusion. Especially elderly patients with preexisting diminished cerebral function may develop profound mental impairment during the postoperative per