The safety impact of the ACGME trainee work hour restrictions remains controversial due to contrasting findings that have suggested benefit, harm, and no significant impact. This observational study analyzed all Medicare patients admitted to acute care facilities with a predefined set of primary diagnoses to estimate the 30-day mortality among high-severity medical admissions and the failure to rescue in postoperative surgical admissions. Investigators found no significant harm or benefit to patients with higher-severity illness compared with those with lower risk among both the medical and surgical patients. A past AHRQ WebM&M perspective discussed the impact of fatigue and extended shifts among trainees on the incidence of medical errors.