It appears that frequency of fractures of the acetabulum is increasing with the number of automobiles on our roads. In the past tell years, several important studies concerning this subject were published. notably those of (Cauchoix and Truchet, Knight and Smith, Stewart and Milford, and Waller. Since 1954, we have paid particular attention to the study of fractures of the acetabulum. Because we were so disappointed with the results of closed treatment of these fractures, we decided to try open reduction. Our series includes 173 patients, of whom 129 were treated surgically. One hundred and eight were operated on primarily (within twenty days after injury) and twenty-one at a later date. Based on these experiences, we wish to describe the mechanism of injury and the roent-genographic and pathological findings in these acetabular fractures and to outline a plan of treatment. of the 17:1 patients in the series, 118 were male and fifty-five were female. The age distribution was fairly uniform— between twenty and sixty years.