Background: Women with diabetes mellitus are at particularly high risk for coronary heart disease-related morbidity and mortality compared with men with diabetes mellitus. However, recent data comparing hospital and long-term outcomes in women with diabetes mellitus and men hospitalized with acute myocardial infarction (AMI) are scarce. The objectives of our multi-hospital observational study were to examine sex differences and temporal trends (1975-99) in hospital and long-term case-fatality rates (CFRs) in patients with diabetes mellitus and AMI from a population-based perspective. Methods: A community-wide study of residents of the Worcester, Mass, metropolitan area who were hospitalized with confirmed AMI was conducted. Data were collected in 12 1-year periods between 1975 and 1999. The study sample consisted of 1354 men and 1280 women with diabetes mellitus. Results: Overall hospital CFRs were significantly greater for women with diabetes mellitus (21.3%) than for men with diabetes mellitus (14.9%). Between 1975 and 1999, hospital CFRs declined from 39.2% to 17.5% for women and from 18.9% to 9.5% in men. In examining long-term survival patterns for as long as 10 years after hospital discharge, there were no significant sex differences in long-term survival rates after adjustment for a limited number of known potentially confounding factors. Conclusions: Hospital death rates after AMI in men and women with diabetes mellitus have declined in the last 2 decades. The gap in hospital CFRs between men and women with diabetes mellitus has decreased considerably with time, although women have a higher risk of dying after AMI than men. Patients with diabetes mellitus continue to represent a high-risk group who will benefit from enhanced surveillance efforts and increased use of effective cardiac treatments.