Long work hours, overnight call duty, and rotating shifts are implicit features of hospital medical practice. Rigorous schedules have been deemed necessary to fulfill the professional obligation of patient beneficence, to optimize trainee learning, and to respond to economic realities. However, the resultant disruption and restriction of physicians' sleep produce demonstrable neurobehavioral impairments that may threaten other fundamental professional mandates, such as that of primum non nocere ("first, do no harm"). This article provides a basic overview of sleep/wake regulatory processes, examines the impact of physician schedules on sleep/wake homeostasis, summarizes the laboratory-demonstrated effects of sleep loss on humans, highlights recent literature on the personal and professional effects of sleep loss on physicians, and, finally, discusses the specific countermeasure of work-hour limits applicable to resident physicians but not attending physicians.