The specific sleep disorders of 97 patients 61-81 years old were compared with those of 264 middle-aged (41-60 years old) and 202 young (20-40 years old) patients. Sleep disorder diagnoses were made according to the Diagnostic Classification of the Association of Sleep Disorders Centers based on evaluations consisting of mental and physical examinations and all-night sleep recordings. Most young and middle-aged patients complained of excessive daytime sleepiness; the elderly complained of insomnia as often as excessive daytime sleepiness. The evaluations revealed objective findings in 93 per cent of the elderly, but only 77 per cent of younger patients. Nocturnal myoclonus or restless leg syndrome was the diagnosed cause of 23 per cent of elderly patients' sleep-wake problems, but only 11 per cent of middle-aged and 4 per cent of young patients had this problem. Respiratory disorders of sleep were found in 27 per cent of elderly, 35 per cent of middle-aged, and 20 per cent of young patients. Elderly patients (6 per cent) had psychiatric disorders diagnosed as the causes for their problems less frequently than did younger patients (22 per cent).