Background Though a few of case reports were published, clinical characteristics of coronary aneurysm associated with drug-eluting stent(DES) are not clear. We investigated the incidence and clinical characteristics of aneurysm formation after DES implantation in DES registry. Methods 1208 consecutive patients who underwent PCI with DES from December 2003 to November 2005 in two referral centers were enrolled. We reviewed the angiographic and procedural data for nine patients who had coronary aneurym after DES implantation. Results The incidence of coronary aneurysm was 0.75%(Total 9/1208, Cypher 7/1015, Taxus 2/193). There were 3 patients with STEMI, 2 patients with NSTEMI, 1 patient with unstable angina, 2 patients with stable angina. Mean diameter and length of aneurysm were 1.76mm(1.4-2.2), 5.68mm(2.5-11.0) on binary measurement. There was no major adverse cardiac event such as acute MI, TLR, cardiac death during follow-up (mean duration 11.2 month) among patients with coronary aneurysm. Conclusion The incidence of aneurysm formation after DES implantation in real world registry was as low as 0.75%. Most of coronary aneurysm after DES implantation were small in size and seems to have good prognosis during follow-up. 66.7% of cases were acute coronary syndrome, suggesting that heavy thrombotic burden might be a risk factor of aneurysm formation after DES implantation.