Aneurysmal dilatation in saphenous vein bypass grafts. Three patients are reported who developed aneurysmal degeneration of a saphenous vein arterial bypass graft. All three had hypercholesterolemia and two had marked elevation of triglycerides. One bypass was for occlusive disease and two for popliteal aneurysm. There was a long lag, 3 to 7 years between graft implantation and aneurysmal degeneration. The pathology was similar for all three cases with lipid laden macrophages, loss of elastic lamina, and other atherosclerotic changes in the vein wall. While atheromatous changes and aneurysm formation in saphenous vein bypass grafts are rare, this may occur especially in patients with hypercholesterolemia and hypertriglyceridemia. Careful and prolonged follow-up plus vigorous management of the hyperlipidemic state is mandatory in these patients. 