Adherence to evidence-based recommendations for acute myocardial infarction (AMI) remains unsatisfactory. Quantifying association between using an electronic AMI order set (AMI-OS) and hospital processes and outcomes. Retrospective cohort study. Twenty-one community hospitals. A total of 5879 AMI patients were hospitalized between September 28, 2008 and December 31, 2010. We ascertained whether patients were treated using the AMI-OS or individual orders (a la carte). Dependent process variables were use of evidence-based care; outcome variables were mortality and rehospitalization. Use of individual and combined therapies improved outcomes (eg, 50% lower odds of 30-day mortality for patients with ?3 therapies). The 3531 patients treated using the AMI-OS were more likely to receive evidence-based therapies (eg, 50% received 5 different therapies vs 36% a la carte). These patients had lower 30-day mortality (5.7% vs 8.5%) than the 2348 treated using a la carte orders. Although AMI-OS patients’ predicted mortality risk was lower (3.2%) than that of a la carte patients (4.8%), the association of improved processes and outcomes with the use of the AMI-OS persisted after risk adjustment. For example, after inverse probability weighting, the relative risk for inpatient mortality in the AMI-OS group was 0.67 (95% confidence interval: 0.52-0.86). Inclusion of use of recommended therapies in risk adjustment eliminated the benefit of the AMI-OS, highlighting its mediating effect on adherence to evidence-based treatment. Use of an electronic order set is associated with increased adherence to evidence-based care and better AMI outcomes.