Recent studies have found an inverse relationship between hospital-specific mortality rates for selected conditions and the number of patients hospitalized with these conditions. These studies have not examined whether this inverse relationship is a result primarily of the nature and volume of services provided to patients by individual physicians or whether it reflects special characteristics of high-volume hospitals. This study examines these issues, using data that link characteristics of primary surgeons to the discharge abstract records of patients. The study analyzes variation in hospital mortality associated with: the total volume of specific surgical procedures performed in the hospital, the volume of these procedures performed by the patient's primary surgeon, physician board certification, and other factors including patient severity of illness, patient age, hospital control, teaching status, size, and location. The findings confirm the inverse relationship found in other studies between patient mortality and the total volume of specific surgical procedures performed in the hospital. Physician board certification and hospital's medical school affiliation also are found to be associated with lower patient mortality rates. However, there is no statistical relationship between the volume of services provided by individual surgeons and outcome, suggesting that the volume-outcome relationship reflects hospital rather than physician characteristics.