Background— The association between low socioeconomic status (SES) and high mortality from coronary heart disease is well-known. However, the role of SES in relation to the clinical outcome after primary percutaneous coronary intervention remains poorly understood. Methods and Results— We studied 7385 patients treated with primary percutaneous coronary intervention. Participants were divided into high-SES and low-SES groups according to income, education, and employment status. The primary outcome was major adverse cardiac events (cardiac death, recurrent myocardial infarction, and target vessel revascularization) at maximum follow-up (mean, 3.7 years). Low-SES patients had more adverse baseline risk profiles than high-SES patients. The cumulative risk of major adverse cardiac events after maximum follow-up was higher among low-income patients and unemployed patients compared with their counterparts (income: hazard ratio, 1.68; 95% CI, 1.47–1.92; employment status: hazard ratio, 1.75; 95% CI, 1.46–2.10). After adjustment for patient characteristics, these differences were substantially attenuated (income: hazard ratio, 1.12; 95% CI, 0.93–1.33; employment status: hazard ratio, 1.27; 95% CI, 1.03–1.56). Further adjustment for admission findings, procedure-related data, and medical treatment during follow-up did not significantly affect the associations. With education as the SES indicator, no between-group differences were observed in the risk of the composite end point. Conclusions— Even in a tax-financed healthcare system, low-SES patients treated with primary percutaneous coronary intervention face a worse prognosis than high-SES patients. The poor outcome seems to be largely explained by differences in baseline patient characteristics. Employment status and income (but not education level) were associated with clinical outcomes.