Natural history of an aneurysm at the bifurcation of the left coronary artery is reported. A gradual increase in its size occurred over an 18-year period until it was a huge and partially thrombosed sac. It was associated with ectasia of the right coronary artery, aneurysms of the left subclavian artery and thoracic aorta, and calcified dilatations of the branches of the celiac trunk.