This report describes the case of a 26-year-old male diagnosed with angina on exertion. A diagnostic coronaryangiography revealed significant luminal narrowing at the middle third of the left anterior descending artery andproximal circumflex artery. The patient underwent implantation of sirolimus-eluting stents. Eight months afterimplantation of the stents, a follow-up coronary angiography showed intrastent coronary artery aneurysms. Wesuggest that the implantation of the sirolimus-eluting stent caused late formation of a coronary artery aneurysm.(Korean Circulation J 2007;37:127-129)