Living alone was reported to be associated with increased risk of cardiovascular disease. There are, however, limited data on the relation between living alone and all-cause mortality in patients with acute myocardial infarction (AMI) undergoing percutaneous coronary intervention (PCI). The Coronary REvascularization Demonstrating Outcome Study in Kyoto (CREDO-Kyoto) AMI registry was a cohort study of patients with AMI enrolled in 26 hospitals in Japan from 2005 through 2007. For the current analysis, we included those patients who underwent PCI within 24 hours of symptom onset, and we assessed their living status to determine if living alone would be an independent prognostic risk factor.