To determine the appropriateness of use of coronary artery bypass graft surgery in New York State.Retrospective randomized medical record review.Fifteen randomly selected hospitals in New York State that provide coronary artery bypass graft surgery.Random sample of 1338 patients undergoing isolated coronary artery bypass graft surgery in New York State in 1990.Percentage of patients who had bypass surgery for appropriate, inappropriate, or uncertain indications; operative (30-day) mortality; and complications.Nearly 91% of the bypass operations were rated appropriate; 7%, uncertain; and 2.4%, inappropriate. This low inappropriate rate differs substantially from the 14% rate found in a previous study of patients operated on in 1979, 1980, and 1982. The difference in rates was not due to more lenient criteria but to changes in practice, the most important being that the fraction of patients receiving coronary artery bypass grafts for one- and two-vessel disease fell from 51% to 24%. Individual hospital rates of inappropriateness (0% to 5%) did not vary significantly. Rates of appropriateness also did not vary by hospital location, volume, or teaching status. Operative mortality was 2.0%; 17% of patients suffered a complication. Complication rates varied significantly among hospitals (P < .01) and were higher in downstate hospitals.The rates of inappropriate and uncertain use of coronary artery bypass graft surgery in New York State were very low. Rates of inappropriate use did not vary significantly among hospitals, or according to region, volume of bypass operations performed, or teaching status.