Eleven patients who had sustained a periprosthetic fracture of the acetabulum at a mean of 6.2 years (range, one month to thirteen years) after a total hip arthroplasty were managed at our institution between 1985 and 1991. Five patients had a fracture of the medial wall; three, a fracture of the posterior column; two, a transverse fracture; and one, a fracture of the anterior column. Six fractures were displaced by two millimeters or more. Eight fractures were caused by blunt trauma or a fall, and three occurred spontaneously. A fracture was classified as type 1 if the acetabular component was clinically and radiographically stable (eight patients) and as type 2 if the component was unstable (three patients).One patient, who had a displaced type-2 fracture of the posterior column, died of an associated intrapelvic vascular injury. The other two patients who had a type-2 fracture were managed with revision of the acetabular component without supplemental plate fixation, immediately after the diagnosis of the fracture. The eight patients who had a type-1 fracture initially were managed with limitation of weight-bearing or modification of activity; in six of these patients, the fracture united without additional treatment.The ten surviving patients were followed for a mean of sixty-two months after the fracture. Eight of these patients—including four in whom a type-1 fracture had united after non-operative treatment—had a revision of the acetabular component because of pain, loosening, or non-union by the time of the most recent follow-up. Two patients (one of whom had a type-1 fracture and the other, a type-2 fracture) had multiple revisions of the acetabular component; both had supplemental internal fixation with a plate. All ten patients ultimately had a stable, functioning prosthesis.We conclude that periprosthetic acetabular fractures are associated with a poor prognosis with regard to the survival of the acetabular component but that it is possible to achieve union and to salvage a functional prosthesis in patients who have sustained such a fracture.