Eighteen (18) obese patients with clinically confirmed obstructive sleep apnea syndrome (OSAS) and five (5) obese persons with no apnea crises noticed during sleep apart from occassional loud snoring, have been polysomnographically assessed. The obtained results show that the patients with apnea syndrome sleep very badly, and consequently, shortened sleep latency and frequent body movements, along with apneas, are regarded as the leading polysomnographic symptoms. Vigilance profile during sleep, that is, interchange and frequency of each of sleep stages (I, II, III, IV, REM) are similar in both tested groups. The suppression of restitutive stages of sleep (III, IV, REM) is considered to be a dominant characteristic of vigilance during sleep in obese persons and obese persons with manifest apnea syndrome. Relatively prolonged sleep latency in obese persons without manifest apnea syndrome indicates, however, restitutively higher quality of their nocturnal sleep. Contrary to the patients with apnea syndrome, they do not suffer from excessive evening somnolence, so that their daily alertness and sleep vigilance during night are of a better quality, although the lack of deep and REM sleep is observed in them as well.