In twenty-one hips of twenty-one patients, the acetabulum was reconstructed using allografts during revision of a total hip arthroplasty. The patients' average age at the time of revision was 64.3 years (range, nineteen to eighty-six years). At an average follow-up of 3.5 years (range, two to five years), three patients had died of causes unrelated to the hip reconstruction, and one had been lost to follow-up. In the other seventeen, the average Harris hip rating was 89 points (range, seventy to 100 points) at follow-up. In one patient the allograft collapsed, so that revision was required. Two patients had asymptomatic progressive radiolucencies at the cement-bone interface of the reconstructed acetabulum, and another had a 1.5-millimeter-wide lucency at the interface of the donor and recipient bone but was asymptomatic, and there had been no change in the position of the cemented acetabular component since operation. The remaining grafts appeared to be incorporated securely, as determined by radiographic examination. Three-dimensional computerized tomographic radioisotopic bone scans showed uniform uptake, consistent with revascularization and new-bone formation, in all grafts. There was no radiographic evidence of focal avascularity and there were no infections. Femoral-head bone allografts appear to provide a useful technique for the reconstruction of a severely deficient acetabulum during revision total hip arthroplasty.