In a prospective study among 5839 consecutive patients after acute myocardial infarction (AMI), the prognosis of men and women with diabetes was compared with that of patients without diabetes after AMI. The prevalence of insulin-treated diabetes or diabetes treated with oral hypoglycemic drugs was 2% and 8% among men and 6% and 12% among women respectively. After multiple regression analysis, the odds ratio for in-hospital mortality was 1.26 (95% confidence interval [CI] 0.82 to 1.92) for non-insulin-treated men with diabetes and 2.24 (95% CI 1.14 to 4.38) for those treated with insulin. Among women, these odds ratios were 1.46 (95% CI 0.90 to 2.36) and 1.80 (0.93 to 3.51), respectively. The 10-year relative risk for death was 1.32 (95% CI 1.10 to 1.58) for men with non-insulin-treated diabetes and 1.75 (95% CI 1.26 to 2.45) for men treated with insulin. For women, the respective relative risks for 10-year mortality were 1.41 (95% CI 1.10 to 1.82) for those treated with oral hypoglycemic drugs and 2.59 (95% CI 1.89 to 3.56) for diabetic women treated with insulin. We conclude that (1) diabetes requiring treatment emerged as an independent predictor of short- and longterm mortality after AMI; (2) diabetic women had a worse long-term prognosis than diabetic men after AMI; and (3) diabetic patients treated with insulin had the worst short- and long-term prognosis after AMI in both genders.