Mortality and morbidity after acute myocardial infarction (AMI) is higher in diabetic than in nondiabetic patients. Angiotensin-converting enzyme (ACE) inhibitors have been shown to exert a beneficial effect after AMI. We sought to evaluate the association between treatment with ACE inhibitors and 1-year outcome after AMI in diabetic and nondiabetic patients in a national survey. The study population was drawn from a national survey conducted in all coronary care units operating in Israel during a 5-month period in 1996, and included 2,179 patients with AMI: 533 diabetics (24%), 322 of whom received ACE inhibitors (60%) and 211 who did not; and 1,646 nondiabetics, 805 of whom received ACE inhibitors and 841 who did not. In both groups of patients, those treated with ACE inhibitors were older, included more women, more had a history of AMI, anterior wall AMI, or hypertension, and more had worse Killip class on admission. Diabetic patients treated with ACE inhibitors experienced lower 1-year mortality rates than diabetics not treated with ACE inhibitors (16.2% vs 18.8%, respectively; covariate adjusted hazard ratio 0.47, 95% confidence interval 0.30 to 0.74). In nondiabetic patients, however, ACE inhibitor treatment was not associated with a better outcome (10.2% vs 7.3%, respectively; covariate adjusted hazard ratio 0.80; 95% confidence interval 0.56 to 1.15). Thus, treatment with ACE inhibitors after AMI appears to be particularly beneficial in diabetic patients. The beneficial effect observed supports the widespread use of ACE inhibitors in diabetic patients after AMI.