Ballet dancers are competitive athletes who undergo extreme physical and mental stress and work according to an irregular schedule, with long days of training, rehearsal, and performance. Their most significant potential risks entail physical injury and altered sleep. The elaborate training requirements for ballet dancers do not allow regular chronobiological patterns or a normal sleep-wake rhythm. Our aim was to investigate the sleep-wake rhythm and sleep quality during rehearsal phases prior to a ballet premiere. We used wrist actigraphy and sleep diaries for a period of 67 days before the ballet premiere performance to study 24 classical ballet dancers. We likewise applied the Epworth Sleepiness Score (ESS), Pittsburgh Sleep Quality Index (PSQI), SF-12 Quality of life Assessment, and d2 Test of Attention to assess quality of sleep, aspects of cognitive performance, and health status. We found significant reduction in sleep duration, from 418+/-43 min to 391+/-42 min, and sleep efficiency, from 81+/-4% to 79+/-5%, over the 67-day course of the rehearsal. We also found a decline in time in bed and an increase in wakefulness after sleep onset. Sleep onset latency did not change. However, the changes in sleep as documented by actigraphy were not reflected by the subjective data of the sleep diaries and sleep scores. As a result of the facts that total sleep efficiency and sleep duration values were already lower than usual for the dancers' age group at the beginning of the study and that mental acuity, concentration, and speed were likewise impaired, we observed exacerbated health deterioration in terms of sleep deprivation in ballet dancers during preparation for a premier. We conclude that individual activity-rest schedules, including daytime naps, may be helpful, especially during the stressful training and rehearsal experienced prior to ballet premieres.