Background Data on clinical characteristics, long-term mortality rates, and factors influencing outcome of acute myocardial infarction (AMI) based on an unselected cohort in the percutaneous coronary intervention (PCI) era are still limited in Japan. Methods and Results In the present study 415 consecutive patients with AMI who were admitted to hospital within 24 h of symptom onset between January 1988 and December 2002 were studied. There was a marked seasonal variation of AMI with a minimum in summer and a maximum in winter, as well as a marked circadian variation with a significant morning peak. Overall, 45.8% of patients were treated with primary PCI. Increased age and female sex were negatively associated with the probability of undergoing PCI. During the follow-up period (mean duration, 4.01±3.41 years), the unadjusted long-term all-cause mortality rate was 21.4%. Multivariate Cox regression analysis showed that age, prior cerebrovascular disease, renal failure, Killip ≥2, and ventricular tachycardia/fibrillation were independent predictors of worse long-term mortality after AMI. Furthermore, the use of PCI was independently associated with favorable long-term survival after AMI. Conclusions Although PCI was associated with a favorable long-term mortality, it remains underused in subsets of patients and increased use may further reduce the long-term mortality rate in Japanese AMI patients. (Circ J 2005; 69: 1170 - 1175)