The results of total hip arthroplasty with the use of medial and superior bone-graft augmentation in thirty-nine hips (thirty-two patients) that had protrusio acetabuli were previously reported after two to eight years (mean, 4.7 years) of follow-up. We followed the surviving patients for 10.9 to 17.4 years (mean, 12.8 years). The average Harris hip-rating was 72 points--an average drop of 17 points since the previous report. The average was 64 points for patients who had rheumatoid arthritis and 83 points for those who had another diagnosis. Radiographic evaluation demonstrated definite, probable, and possible loosening in about 20, 10, and 60 per cent of the hips, respectively. Of the six hips that had definite loosening, four (10 per cent of the total series) had progression of the protrusion (acetabular migration); operative revision was performed on two of those four hips and on two other hips, in which progression had ceased. Hips that had progressive protrusion demonstrated superior migration more often than medial migration. The rates of loosening and revision were similar to those in hips that did not have protrusio acetabuli. We concluded that augmentation of total hip arthroplasty with bone-grafting is effective in arresting the progression of protrusio acetabuli in most hips (90 per cent in our series).