Although numerous studies indicate that women have a higher early mortality from acute myocardial infarction (AMI) than men, reasons for the difference are largely unexplained. We studied the role of sex in the prognosis of 1,600 patients with AMI aged 30 to 74 years in the population-based Minnesota Heart Survey. A 50% random sample was taken of all AMI patients hospitalized in 1980 and 1985 in the Twin Cities of Minnesota (Minneapolis-St. Paul) (1,168 men, 432 women). A multiple logistic regression model was used for predicting early death (within 28 days) and included baseline characteristics: sex, age, chest pain on admission, history of previous AMI, angina pectoris, coronary artery bypass surgery or hypertension, presence of heart failure, cardiac arrhythmias requiring direct-current shock, diabetes mellitus, valvular disease, cardiomyopathy, and levels of serum enzymes and blood urea nitrogen. Age-adjusted early mortality rate was significantly higher in women than men, but only in those aged < 65 years (12.5% of women vs 6.5% of men, p < 0.01) versus those aged > or = 65 years (19.5% vs 21.6%, p > 0.05). Multivariate analysis also showed that among those < 65 years, female sex was a strong and independent predictor of early death (odds ratio 2.0, 95% confidence interval 1.2 to 3.5, p < 0.01). Rates of coronary angiography, coronary artery bypass surgery, percutaneous transluminal coronary angioplasty, and thrombolysis performed during hospital stay were higher in men, but after adjustment for age, congestive heart failure, and diabetes mellitus, a statistically significant difference persisted only in the frequency of coronary angiography (26% in men vs 17% in women, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)