This study attempted to evaluate the effect of the Accreditation Council for Graduate Medical Education (ACGME)'s 2003 regulations limiting housestaff work hours on mortality among Medicare inpatients. The authors analyzed more than 8 million admissions for a 5-year period spanning implementation of the regulations. No statistically significant change in mortality was found at teaching hospitals for either medical or surgical patients. A companion study by the same authors, however, did find statistically significant mortality reductions for medical inpatients (but not surgical patients) at Veterans Affairs (VA) hospitals, especially those with a higher concentration of residents. Previous research on this matter also found no improvement in mortality for medical patients (but no evidence of harm). Taken together, these studies seem to indicate little overall effect of duty hours reforms on inpatient mortality. A related editorial discusses the need for more research on the effect of work hour limitations on patient outcomes before additional restrictions are considered.