This report describes the case of a 45-year-old Korean female who had suffered from Behçet's syndrome for two years with a huge, unruptured aneurysm originating from the left coronary sinus. The aneurysm had caused myocardial and aortic insufficiency by compressing the proximal left anterior descending coronary artery. The orifice of the aneurysm was at the left coronary sinus, about 5 mm from the left main coronary ostium, and it was filled with organized thrombi. Surgical repair was performed by closing the entrance of the aneurysm with a Dacron patch and by implementing aortic valve repair and coronary artery bypass grafting. The patient's coronary flow was restored postoperatively, and all anginal symptoms disappeared.