A 40-year-old man was referred to our hospital because of an abnormal shadow on the left cardiac border on the chest roentgenogram at the regular medical health examination without any symptoms. A giant coronary artery aneurysm of left anterior descending artery with a maximum diameter of approximately 50 mm was detected with computed tomography and coronary angiography. The patient was treated and followed up medically. Four years later, the size of the coronary artery aneurysm became larger. Then resection of the coronary artery aneurysm and coronary artery bypass grafting were successfully performed. Coronary artery aneurysms are rare in adults and are usually found in association with Kawasaki disease, coronary atherosclerosis, and so on. We also review the literature of giant coronary artery aneurysms exceeding 50 mm in diameter.