The average number of hours worked annually by workers in the United States has increased steadily over the past several decades and currently surpasses that of Japan and most of Western Europe. The influence of overtime and extended work shifts on worker health and safety, as well as on worker errors, is gaining increased attention from the scientific community, labor representatives, and industry. U.S. hours of service limits have been regulated for the transportation sector for many years. In recent years, a number of states have been considering legislation to limit mandatory overtime for health care workers. The volume of legislative activity seen nationwide indicates a heightened level of societal concern and the timeliness of the issue. This document summarizes recent scientific findings concerning the relationship between overtime and extended work shifts on worker health and safety. The number of studies increased dramatically over the past few years, but important research questions remain. I am confident that this document will contribute to an informed discussion of these issues and provide a basis for further research and analysis. This report provides an integrative review of 52 recently published research reports that examine the associations between long working hours and illnesses, injuries, health behaviors, and performance. The report is restricted to a description of the findings and methods and is not intended as an exhaustive discussion of all important issues related to long working hours. Findings and methods are summarized as reported by the original authors, and the study methods are not critically evaluated for quality.