Resident physician duty hour regulations have primarily been driven by an impetus to improve patient safety, but evidence supporting this effect is largely lacking. This observational study compared patient outcomes between a resident medicine service and hospitalist (nonresident) medicine service at a large academic medical center, before and after the 2011 ACGME work hour reforms. Overall there were no significant differences in length of stay, 30-day readmission, inpatient mortality, hospital-acquired conditions, or intensive care unit admissions. A New England Journal of Medicine roundtable discussion explored the past decade of duty hour reforms, and a recent commentary by Drs. Halpern and Detsky called for more research evaluating the intended and unintended effects of these mandates. An AHRQ WebM&M perspective reviewed evidence surrounding the impact of resident duty hour limits on safety in health care.