Salient histopathological features in 13 failed free vascularized fibular autografts implanted for osteonecrosis of the femoral head are documented. Of particular clinical and/or biomechanical relevance are 1-2-mm-thick seams of viable lamellar bone bonded circumferentially to anatomically intact but necrotic graft cortices, which appear to preclude their revascularization and remodeling. Surrounding the grafts are 3-6-mm-thick rings of reactive bone, fused in many sites (average approximately 54%) to the osseous seams. They consist of a layer of sclerotic cortical-like bone melded with an outer layer of thickened cancellous bone. This remodeled reactive bone, largely the result of drilling, appears to buttress the grafts structurally and by inference, functionally. Operative failures in all but one case are attributed primarily to collapse of the necrotic, fractured superior subtending segment of the graft and of the subchondral plate secondary to size and progression of the osteonecrosis and superimposed osteoarthrosis. Morphological integrity of grafts elsewhere and perifibular reactive sclerotic bone remain unimpaired for up to 5 1/2 years. The salutary features of vascularized autografts would appear to give them a decided advantage over their nonvascularized counterpart.