A total of 237 patients with surgically treated acetabular fractures were analyzed to identify the risk factors predisposing to development of heterotopic ossification (HO) following operative treatment, and to evaluate both clinical significance of HO and the clinical outcome of operative excision of ectopic bone. AH patients had a minimum of 1 year followup time. The degree of HO was determined from anteroposterior radiographs of the pelvis at the 1 year followup and was classified as Grade 0 or Grade 1 according to the amount of ectopic bone present. Forty patients (17%) who developed a moderate to severe amount of ectopic bone were classified as Grade 1. Nine who developed significant ectopic bone resulting in 20% or greater loss of hip motion underwent excision of the ectopic bone; all six available for followup showed an improvement in range of motion. A significant correlation was found between poor clinical results at the 1 year followup and Grade 1 ectopic bone formation (p < 0.001). Four factors found to highly correlate with Grade 1 ectopic bone formation were: (1) the iliofemoral surgical approach; (2) multiple (2 or more) operative findings; (3) T type fractures; and (4) the presence of associated injuries to the abdomen and chest.