Background: Cystatin C is reportedly a better endogenous marker of glomerular filtration rate than serum creatinine, so the prognostic value of cystatin C in patients with ST-elevation myocardial infarction (MI) was evaluated in the present study. Methods and Results: A total of 71 patients who underwent percutaneous coronary intervention for ST-segment elevation MI <24 h from symptom onset were included. According to cystatin C level, patients were classified into 2 groups: (1) higher cystatin C group (n=33) and (2) lower cystatin C group (n=38). There was a trend toward more in-hospital deaths in patients with the higher cystatin C level compared with the lower cystatin C level group (15.2% vs 2.6%, P=0.06). Mean duration of clinical follow-up was 5.6 ±2.8 months. There was no significant difference in death, reinfarction, disabling stroke or target lesion revascularization between the 2 groups. However, a higher incidence of rehospitalization for congestive heart failure was observed in patients with the higher cystatin C level than in those with the lower cystatin C level (15.2% vs 0%, P=0.01). Conclusions: Cystatin C may be associated with more cardiovascular events, mainly rehospitalization for congestive heart failure, after percutaneous coronary intervention in patients with ST-elevation MI. (Circ J 2009; 73: 1669-1673)