Background: Knowledge of the location of the weight-bearing portion of the acetabulum would assist orthopaedic surgeons in the treatment of acetabular fractures. With use of controlled experimental transverse, anterior column, and posterior column osteotomies, we investigated the weight-bearing region of the acetabulum.Methods: Twenty-four fresh-frozen cadaveric hip joints were tested. Simulated transverse fractures were evaluated in twelve specimens, and simulated anterior column and posterior column fractures were tested in six specimens each. Each femur and acetabulum was potted and mounted in an aluminum fixture, with the acetabulum positioned in 25 degrees of flexion and 20 degrees of abduction. Each specimen was tested intact and after successive osteotomies. The transverse osteotomies had roof-arc angles of 60, 50, 40, and 30 degrees. The anterior column and posterior column osteotomies were classified as very low, low, intermediate, or high. Compressive loading to 800, 1200, and 1600 newtons was performed four times for each intact specimen and after each osteotomy. A specimen was considered to be stable if no gross dislocation occurred during any of the four loading cycles. Translation of the femur within the acetabulum also was measured during each trial.Results: The number of stable specimens decreased both with higher applied loads and with more superior osteotomies. The stability of the hip was significantly affected by both the location of the fracture and the magnitude of the applied load (p < 0.00005). Translation of the femur within the acetabulum increased with higher applied loads and with more superior osteotomies.Conclusions: Fractures that have a medial roof-arc angle of 45 degrees or less, an anterior roof-arc angle of 25 degrees or less, or a posterior roof-arc angle of 70 degrees or less cross the weight-bearing portion of the acetabulum and necessitate operative treatment.Clinical Relevance: Fractures exiting the posterior column just superior to the ischial spine and those exiting the anterior column through the iliac wing lead to instability. When a patient has a displaced fracture crossing this area, every effort should be made to achieve anatomical reduction in order to prevent posttraumatic arthritis.