To investigate the prevalence of excessive daytime somnolence and contributing factors, 58,162 draftees between 17 and 22 years of age, registered in two selection centers of the French army, were screened by means of a 17-item questionnaire. In response, 8,201 subjects (14.1%) reported occasional daytime sleep episodes, 2,210 (3.8%) one or two daily episodes, and 640 (1.1%) more than two daily episodes. Of the total sample, five percent or 2,933 considered these sleep episodes to affect their lives. Different possible factors of daytime sleep episodes were investigated, including hours of nocturnal sleep, sleep-wake schedule, sleep difficulties, use of hypnotics, snoring, and occurrence of cataplexy. A strong association was found between these factors and excessive daytime somnolence. A stepwise multivariate analysis was performed on five of these factors: hours of nocturnal sleep, sleep-wake schedule, sleep difficulties, use of hypnotics, and snoring. All five factors were shown to be independently related to excessive daytime somnolence and were ranked in the following descending order: use of hypnotics, sleep difficulties, irregular sleep-wake schedule, snoring, and hours of sleep.