Twenty-four hour ambulatory sleep-wake recordings were made in 10 untreated patients with narcolepsy-cataplexy and 10 matched controls. Nocturnal sleep of narcoleptics was similar to descriptions of laboratory based recordings and was characterized by frequent sleep onset REM periods, high variability of REM latency, increased amounts of wakefulness after sleep onset, and low sleep efficiencies. Daytime portions in narcoleptics showed greater drowsiness and sleep than in controls with significantly higher amounts of stages 1A, 1B, 3, 4 and REM, more sleep episodes longer than 1 and longer than 10 min in duration, and high intersubject variability. On average, only 1.2 daytime sleep episodes began with sleep onset REM periods. There was a strong tendency in both groups towards a long mid-afternoon sleep episode often containing slow wave sleep (SWS) and which was significantly longer in narcoleptics. The mean interval between the onset of nocturnal SWS and the main daytime SWS peak was 14.1 h for narcoleptics and 13.6 h for controls. Daytime waking portions in narcoleptics showed significantly less 'active wakefulness' than in controls. There was no correlation between MSLT measures of sleepiness and amount of daytime sleep in ambulant recordings.