Reduced sleep time is commonplace for many interns and residents. Recent studies, however, suggest that sleep loss and fatigue result in significant neurobehavioral impairments in healthy young adults. We reviewed studies addressing the effects of sleep loss on cognition, performance, and health in surgical and nonsurgical residents. We describe the effectiveness of countermeasures for sleepiness, including recent work-hour restrictions. A more complete understanding of the issues of sleep loss during residency training can inform innovative strategies to minimize the effects of sleepiness and fatigue on patient care and resident safety.