Background: While a couple of case reports were published, the long-term fate of coronary artery aneurysm associated with drug-eluting stent (DES) has not been clearly understood. We assessed clinical and angiographic characteristics, and the outcomes of coronary artery aneurysm developed in DES-implanted lesions. Methods: 1,339 consecutive patients (3,406 target lesions) undergoing DES implantation (2,602 sirolimus-eluting [SES] and 806 paclitaxel-eluting stents [PES]) and follow-up angiography 6-9 months after implantation were enrolled in three referral centers, with baseline, procedural, and outcome registry data. Coronary artery aneurysm was defined as ectatic segment of stented coronary artery with luminal diameter greater than 1.5 times of reference diameter after successful DES implantation. Results: Among 3,406 DES-implanted lesions, a total of 20 lesions (0.58%) of coronary artery aneurysms occurred; 15 lesions in 12 SES-implanted patients and 5 lesions in 5 PES-implanted patients. While clinical status of ischemic heart disease in time of DES implantation was not predictive of coronary artery aneurysm formation (9 in acute coronary syndrome and 8 patients in stable angina), lesion characteristics were predictive (17 in type B2 and C lesions, and 3 in type A and B1). During the follow-up period, there was no adverse coronary event in 16 patients with coronary artery aneurysm on prolonged clopidogrel. Acute myocardial infarction with angiographically-proven stent thrombosis occurred in one patient 16 months after SES implantation, in whom clopidogrel had been discontinued since 9-month follow-up angiography showing patent stent despite aneurysm formation. Conclusions: This study demonstrates that the coronary artery aneurysms after DES implantation, which might be closely associated with lesion complexity, are rarely developed in real world. However, this data supports the extended maintenance of dual antiplatelet therapy including clopidogrel even though DES-associated aneurysms have relatively favorable outcome.