Studies from a variety of settings have indicated that outcomes for coronary angioplasty are improved when performed in institutions with high caseloads (>400/year). The purpose of this investigation was to examine the volume outcome hypothesis for coronary angioplasty in a 20% stratified sample of acute care, non-federal hospitals in 17 states. Data were derived from the Nationwide Inpatient Sample from the Health Care Cost and Utilization Project releases 2 and 3. From these records, 163,527 angioplasties from 214 hospitals were selected. Outcomes included hospital mortality, same-admission coronary artery bypass surgery, and a combined end point of either death or same-admission surgery, or both. Hospital volumes were defined as low (≤200 cases/year), medium (201 to 400), and high (>400). Analyses were conducted separately for patients with and without a principal discharge diagnosis of acute myocardial infarction (AMI). For both AMI and no-AMI groups, the rates of adverse outcomes were generally lower in high-volume institutions, and this finding was true in both univariate and multivariate analyses. Although 27% of hospitals were in the low-volume category, only 5% of all procedures were performed in these institutions. Projecting to all United States hospitals for the 2 years, if all procedures performed in low-volume centers had been done in high-volume institutions, 137 deaths could have been averted (90 AMIs, 47 no-AMIs) as well as 404 (46 AMIs, 358 no-AMIs) same-admission surgeries. The results of this study support the hypothesis that better results are obtained in higher volume institutions, but also show that in 1993 and 1994, relatively few patients had their procedures performed in low-volume institutions.