Sleep-wake habits and control of postural muscle tone were investigated by self-report questionnaire in 183 subjects considered to have the narcoleptic syndrome, 62 subjects with hypersomnia and 10 with obstructive sleep apnoea. Results were compared with those in a group of 188 control subjects with normal sleep wake habits. Excessive daytime sleepiness, determined by the Epworth Sleepiness Scale (ESS), was five times greater in the narcoleptic syndrome than in control subjects (score range 0-24, mean scores +/-SD 19.6+/-3.0; and 4.5+/-3.3 respectively; P<0.001). The propensity to cataplexy, as determined by a rating scale developed to estimate the likelihood of loss of postural tone in response to sudden emotional stimuli, including laughter, was 10 times greater in narcoleptic syndrome than in control subjects (postural atonia total score range 0-600; mean + SD 334+/-122 and 28+/-45, respectively; P<0.001). Narcoleptics had more disturbances of night sleep than controls with episodes of muscle jerking, sleep walking, sleep talking and sleep terrors, as well as sleep paralysis, and higher insomnia self-rating scores. Sleep latency from bedtime to sleep-onset time was shorter in narcoleptics than controls. The hypersomniac group of 62 subjects was heterogeneous. Subsequent investigation showed that 18 subjects (29%) had idiopathic hypersomnia, four (6%) 'incomplete' narcolepsy without cataplexy and 10 (16%) hypersomnia accompanying a mood disorder. The mean ESS scores in this group and in subjects with obstructive sleep apnoea were comparable to those of the narcoleptic syndrome subject group. Mean postural atonia scores were similar to those of control subjects.