This report describes the case of a 62-year-old woman who was previously diagnosed with stable angina. Coronary angiography revealed clinically significant stenosis in the middle of the left anterior descending (LAD) artery, the first diagonal branch, the distal left circumflex (LCX) artery and the proximal posterior descending artery (PDA). After administering aspirin and clopidogrel, the patient underwent implantation of sirolimus-eluting stents in the middle LAD artery and the first diagonal branch. Bare-metal stents were implanted in the distal LCX artery and the proximal PDA. Nineteen months later, follow-up coronary angiography revealed aneurysmal dilation at the middle LAD artery and the first diagonal branch. Forty-six months after implantation of the sirolimus-eluting stents, the size of the coronary aneurysm had increased to 12.4 mm; however, no sign of aneurysmal dilatation was observed at the bare-metal stent sites. This suggested that the implantation of the sirolimus-eluting stent was partially responsible for causing the coronary aneurysm.