Objective: The purpose of this study was to document trends in the prevalence of diabetes among men and women hospitalized for myocardial infarction (MI) and to determine the effect of diabetes on in-hospital case fatality rates and long-term survival. Research Design and Methods: The Minnesota Heart Survey is a population-based surveillance system that has monitored trends in coronary heart disease morbidity since 1970. As part of this effort, a 50% random sample of acute MI discharge records in Minneapolis-St. Paul metropolitan area hospitals was abstracted in 1970, 1980, and 1985. Results: The prevalence of diabetes among MI patients was compared over time, and the data indicated a significant increase between 1970 and 1985 in both men (8.2 vs. 16.8%, P < 0.001) and women (16.0 vs. 25.8%, P = 0.01). Diabetic individuals had an odds ratio of in-hospital death after an MI 1.5 times that of nondiabetic individuals (P < 0.01) after controlling for the effects of sex, age, and year of MI. Among discharged MI survivors, the risk of death was 40% higher (P < 0.01) in diabetic individuals than nondiabetic individuals after 6 yr of follow-up. Compared with nondiabetic individuals, diabetic individuals appeared more likely to have cardiac (pump) failure with acute MI. Conclusions: Our findings suggest that the risk of coronary heart disease morbidity and mortality attributable to diabetes may be increasing over time. Therefore, clinicians need to take extra care in the management of MIs in diabetic individuals, and public health efforts to reduce diabetes prevalence are warranted.