BACKGROUND It has been known for nearly 20 years that, in cardiovascular operations, a significant inverse relationship exists between clinical outcomes and the volume of procedures performed. Interestingly, this relationship persists 2 decades after it was recognized. OBJECTIVE The purpose of this study was to examine the relationship between hospital volume and in-hospital deaths in 3 cardiovascular procedures: coronary artery bypass grafting, elective repair of abdominal aortic aneurysms, and repair of congenital cardiac defects. METHODS The database includes all patients who were hospitalized in New York State during the years 1990 to 1995. Using standard logistic regression techniques, we analyzed the relationship between hospital volume and outcome. RESULTS No correlation exists between hospital volume and in-hospital deaths in coronary artery bypass grafting. Statewide, 31 hospitals performed 97,137 operations over the 6-year period (overall mortality rate, 2. 75%). By contrast, most of the hospitals statewide (195 of 230 hospitals) performed 9847 elective abdominal aortic aneurysm repairs with an overall mortality rate of 5.5%. In abdominal aortic aneurysm operations, a significant inverse relationship between hospital volume and in-hospital deaths was determined. Sixteen hospitals performed 7199 repairs for congenital cardiac defects. A significant inverse relationship (which was most pronounced for neonates) was found between volume and death. CONCLUSIONS The importance of these findings lies in the rather striking difference between the volume-outcome relationship found for operations for abdominal aortic aneurysms and congenital cardiac defects and the lack of such a relationship for coronary artery bypass grafting. This observation may be largely explained by the quality improvement program in New York State for bypass operations since 1989. If so, these results have important implications for expanding the scope of quality improvement efforts in New York State.