Coronary artery dissection is a devastating disease, but spontaneous left main coronary artery dissection is extremely rare. We present the case of a 58-year-old diabetic man who was found to have primary spontaneous left main coronary artery dissection during a coronary angiography examination. Although the dissecting lesion persisted, he had no peri-procedural chest discomfort or electrocardiographic change. We performed urgent coronary artery bypass grafting, which was uneventful. The patient received regular cardiovascular follow-up and did not complain of any postoperative chest discomfort. He had an uneventful recovery.