Human beings, like other living organisms, have physiologic systems that are cyclic in nature. Many of these systems have a circadian length. This provides for internal stability while at the same time enabling the organism to interact with the external environment and respond to changes in that environment. These physiologic systems, including those with a circadian length, can change timing as a result of environmental cues, such as the light-dark cycle or seasonal variations, but this takes time. When people engage in rotating or night shift work, the circadian rhythms are unable to quickly adapt to a rapidly changing activity schedule. This results in desynchronosis of many physiologic systems, including those with circadian timing. Because many emergency physicians engage in shift work, they are subject to the effects of circadian rhythm disruption. Research on the effect of desynchronosis on emergency physicians is sparse but has demonstrated negative effects. This article reviews the effect of desynchronosis on the health and productivity of physicians engaged in shift work.