Late unilateral limb thrombosis was encountered in 45 of 601 patients discharged from the hospital with functioning aortic bifurcation grafts, an incidence of 7.5%. It was invariably associated with clinical manifestations of arterial insufficiency to the affected limb more serious than those of the extremity prior to the initial operation. Although the specific cause could not be determined, it was usually due to either progression of the disease distal to the reconstructed segment or to certain compromises at the time of the first operation or both. Among several procedures employed, unilateral reconstruction of the thrombosed limb is the procedure of choice. The reoperation was successful in 75% of the patients.