Concern is frequently expressed by health care providers and consumers that the work environment of physicians-in-training may adversely affect their performance. This article documents the effects of changing from a traditional rotational overnight call schedule for house staff to a schedule designed to reduce sleep deprivation, distribute admissions more evenly throughout the week, and improve continuity of inpatient care on the internal medicine service of a large, university-affiliated Veterans Affairs Medical Center. In a prospective, time-series study, the hypothesis that this change would improve the efficiency and quality of medical care was evaluated by comparing the hospital course of the patients admitted during 4-week periods prior to and following the change in work schedule. The patients in the preintervention group do not differ significantly from those in the postintervention group in any identifiable clinical characteristics. The length of stay was shorter (10.9 vs 9.3 days) and the number of laboratory tests ordered per patient was smaller (24.0 vs 19.0) for patients cared for under the new work schedule compared with those cared for under the traditional work schedule. Resident physicians also committed fewer medication errors under the new work schedule (16.9 vs 12.0 per 100 patients discharged). We conclude that altering the house staff work schedule affects patient care and can lead to a decrease in utilization of health care resources.