BACKGROUND: The “Swiss cheese model” of systems accidents is commonly applied to patient safety, implying that many “holes” must align before an adverse event occurs. The Accreditation Council for Graduate Medical Education (ACGME) instituted work hour limitations to fill one such hole by reducing resident fatigue. OBJECTIVE: The objective of this study was to determine how residents perceive the impact of the ACGME rules and other factors on patient safety. DESIGN: The study was designed as a focus group study. PARTICIPANTS: Participating in the study were 28 internal medicine residents, of whom 13 were from a university-based program that includes both an academic medical center and a Veterans Affair (VA) hospital, 9 were from a co...