This study present an easy and practical subjective method for evaluating vigilance disorders: the sleep diary. We used it in hypersomnia and deficits of waking. Sleep diaries were filled in by 10 control and 22 hypersomniac subjects. Twentyfour hour polyhypnographic recording allowed the classification of hypersomnia as 13 narcolepsies, 9 hypersomnias with a prevalence of PS, 2 ‘harmonious’ hypersomnias and 1 waking deficit. The sleep diary data (amount of nocturnal sleep and diurnal sleep onset and vigilance decrease) were compared with polygraphic results. According to the diary data, 3 groups of hypersomnia appeared with regard to the time at which sleep onset occurred. The first group presented an increase of sleep onsets at 2 p.m. In the second group, almost exclusively composed of narcoleptic subjects, sleep onsets occurred every 2 h and in the third group they were distributed throughout the day. These results suggest different physiological mechanisms for these 3 groups of hypersomnia. Finally, the sleep diary seems to be an easy and cheap method of evaluating vigilance disorders in hypersomniac subjects during their everyday life.