This review discusses evidence for the role sleep deprivation plays on performance in both laboratory and clinical settings. The authors define sleep deprivation and summarize past research that suggests the impact is greatest on mood and cognitive tasks rather than motor tasks. They also summarize how fatigue can diminish clinical performance and why this factor poses a significant patient safety concern. Implications from their findings call for greater attention to fatigue in clinical settings and the importance of physicians' acknowledging such states as a risk to their patients rather than a sign of personal weakness. Following publication of this review, two studies evaluated the same relationship in anesthesiology residents and medical interns.