Background-This study assessed sex differences in treatments, all-cause mortality, relative survival, and excess mortality following acute myocardial infarction. Methods and Results-A population-based cohort of all hospitals providing acute myocardial infarction care in Sweden (SWEDEHEART [Swedish Web System for Enhancement and Development of Evidence-Based Care in Heart Disease Evaluated According to Recommended Therapies]) from 2003 to 2013 was included in the analysis. Excess mortality rate ratios (EMRRs), adjusted for clinical characteristics and guideline-indicated treatments after matching by age, sex, and year to background mortality data, were estimated. Although there were no sex differences in all-cause mortality adjusted for age, year of hospitalization, and comorbidities for ST-segment-elevation myocardial infarction (STEMI) and non-STEMI at 1 year (mortality rate ratio: 1.01 [95% confidence interval (CI), 0.96-1.05] and 0.97 [95% CI, 0.95-.99], respectively) and 5 years (mortality rate ratio: 1.03 [95% CI, 0.99-1.07] and 0.97 [95% CI, 0.95-.99], respectively), excess mortality was higher among women compared with men for STEMI and non-STEMI at 1 year (EMRR: 1.89 [95% CI, 1.66-2.16] and 1.20 [95% CI, 1.16-1.24], respectively) and 5 years (EMRR: 1.60 [95% CI, 1.48-1.72] and 1.26 [95% CI, 1.21-1.32], respectively). After further adjustment for the use of guideline-indicated treatments, excess mortality among women with non-STEMI was not significant at 1 year (EMRR: 1.01 [95% CI, 0.97-1.04]) and slightly higher at 5 years (EMRR: 1.07 [95% CI, 1.02-1.12]). For STEMI, adjustment for treatments attenuated the excess mortality for women at 1 year (EMRR: 1.43 [95% CI, 1.26-1.62]) and 5 years (EMRR: 1.31 [95% CI, 1.19-1.43]). Conclusions-Women with acute myocardial infarction did not have statistically different all-cause mortality, but had higher excess mortality compared with men that was attenuated after adjustment for the use of guideline-indicated treatments. This suggests that improved adherence to guideline recommendations for the treatment of acute myocardial infarction may reduce premature cardiovascular death among women.