IMPORTANCE Hospitalist physicians face increasing pressure to maximize productivity, which may undermine the efficiency and quality of care. OBJECTIVE To determine the association between hospitalist workload and the efficiency and quality of inpatient care. DESIGN, SETTING, AND PARTICIPANTS We conducted a retrospective cohort study of 20 241 admissions of inpatients cared for by a private hospitalist group at a large academic community hospital system between February 1, 2008, and January 31, 2011. EXPOSURES Daily hospitalist workload as measured by relative value units and patient encounters from the hospitalist billing records. MAIN OUTCOMES AND MEASURES The main outcomeswere length of stay (LOS), cost, rapid response team activation, in-hospital mortality, patient satisfaction, and 30-day readmission rates. Key covariates included hospital occupancy and patient-level characteristics. RESULTS The LOS increased as workload increased, particularly at lower hospital occupancy. For hospital occupancies less than 75%, LOS increased from 5.5 to 7.5 days as workload increased. For occupancies of 75%to 85%, LOS increased exponentially above a daily relative value unit of approximately 25 and a census value of approximately 15. At high occupancy (>85%), LOS was J-shaped, with significant increases at higher ranges of workload. After controlling for LOS, cost increased by 111 for each 1-unit increase in relative value unit and 205 for each 1-unit increase in census across the range of values. Changes in workload were not associated with the remaining outcomes. CONCLUSIONS AND RELEVANCE Increasing hospitalistworkload is associated with clinically meaningful increases in LOS and cost. Although our findings should be validated in different clinical settings, our results suggest the need formethods to mitigate the potential negative effects of increased hospitalist workload on the efficiency and cost of care.