The authors present a new mechanical exercise splint for the hip. The appliance carries out movements in three dimensions and is used early in the postoperative period following surgical treatment of the hip and surrounding structures for continuous passive motion (CPM) treatment. When the hip is flexed, the knee bends at the same time. It is possible, however, for the part of the leg cradle that holds the lower leg to be locked in the extended position to avoid any problems for patients with arthrodesis in the knee. It is also advisable for knee movement to be blocked when the patient does exercises involving spreading and closing of the legs and inward and outward rotation. In this case the leg concerned should be bent about 10 degrees at the hip to avoid friction losses against sheets and mattress. The main indications for use of the new splint are internal fixation following acetabular fractures, periacetabular fractures, dislocation, joint fractures with dislocation of the same joint and fractures or pseudarthrosis at the upper end of the femur. Other appropriate forms of treatment are synovectomy, surgery to improve the form of the cup, including pelvic osteotomy, all kinds of transformation osteotomy, especially for hip necrosis or osteochondrosis dissecans, soft tissue surgery such as capsulotomy, tenotomy or resection following ectopic bone formation and flaccid paralysis.(ABSTRACT TRUNCATED AT 250 WORDS)