Important determinants of incomplete ST-segment recovery in patients undergoing primary percutaneous coronary intervention (PCI) for ST-segment elevation myocardial infarction (STEMI) have been incompletely characterized. Early risk stratification could identify patients with STEMI and incomplete ST-segment recovery who may benefit from adjunctive therapy. For the present study, we analyzed 12-lead electrocardiograms from 2,124 patients with STEMI who underwent primary PCI at our institution from 2000 to 2007. ST-segment recovery was defined as percent change in cumulative ST-segment deviation between preprocedural and immediately postprocedural electrocardiograms and categorized as incomplete when <50%. A total of 1,032 patients (49%) had incomplete ST-segment recovery. After multivariable adjustment, age >60 years (adjusted odds ratio [OR] 1.28, 95% confidence interval [CI] 1.06 to 1.54, p = 0.011), diabetes mellitus (OR 1.36, 95% CI 1.02 to 1.82, p = 0.034), left anterior descending coronary artery-related STEMI (OR 1.92, 95% CI 1.61 to 2.30, p<0.001), and multivessel disease (OR 1.34, 95% CI 1.10 to 1.63, p = 0.004) were independent predictors of incomplete ST-segment recovery. Current smoking (OR 0.79, 95% CI 0.65 to 0.95, p = 0.013) and a preprocedural Thrombolysis In Myocardial Infarction grade <3 flow (OR 0.70, 95% CI 0.53 to 0.93, p = 0.014) were inversely related to ST-segment recovery. Incomplete ST-segment recovery was a strong predictor of long-term mortality (hazard ratio 2.07, 95% CI 1.59 to 2.69, p <0.001) in addition to identified characteristics that independently predicted incomplete ST-segment recovery. In conclusion, incomplete ST-segment recovery at the end of PCI occurred significantly more often in the presence of an age >60 years, nonsmoking, diabetes mellitus, left anterior descending coronary artery-related STEMI, multivessel disease, and preprocedural Thrombolysis In Myocardial Infarction grade 3 flow. Patients with STEMI and these clinical features are at increased risk of impaired myocardial salvage and are appropriate candidates for adjunctive therapy.