On first glance, it seems self-evident: sleep-deprived physicians-intraining (residents) are more likely to make mistakes that could harm patients. Like pilots and truck drivers, these new physicians might need restrictions on how much they work. Such restrictions were created in 2003, but the impact of these new rules is unclear. Are patients any safer? Is hospital care more fragmented? Who’s doing the work that residents performed prior to duty hour reform? This Issue Brief summarizes several studies that offer evidence about the impact of these regulations on patient mortality, as well as on residents’ perceptions of the effects on quality of care, medical education, and residents’ quality of life.