Sleep-wake patterns in 10- and 14-year-old children were followed over a year using sleep diaries kept during 2-week periods every 5 weeks. The times of awakening and sleep duration closely followed the annual and weekly alternations of schooldays and holidays. During vacations, sleep duration increased considerably as compared to the school year. The clear decrease in sleep duration was observed in spring only for 14-year-olds. Weekly changes of sleep patterns during the school year disappeared during vacations. It was concluded that sleep duration in children is closely related to the school schedules and could be a result of sleep deprivation and recovery.