We analyzed the records of 103 conventional hip arthroplasties in seventy-five active patients who were between the ages of forty and sixty years. After five to ten years of follow-up, an excellent or good clinical result was evident in 90 per cent. The radiographic appearance of the cement-bone interface of the acetabular component was stable in those hips, and no progressive acetabular radiolucency was found in 80 per cent of the hips. Of twenty hips with a complete acetabular radiolucency (Grade III or IV), only three had a secondary revision operation, two in conjunction with a fracture of the stem of the prosthesis and one for migration (Grade IV). Eight additional hips showed migration. Seventy per cent of the femoral components were well fixed, without radiographic evidence of loosening. A fracture of the femoral stem occurred in eight hips, all of which had a revision operation. One revision operation was done for loosening of the femoral stem. Seven femoral stems showed either shift or subsidence. An isolated radiolucency in the superolateral zone was present in four hips and an isolated lucency in other zones, measuring one millimeter or less, was present in ten hips. Thus, radiographic evidence of loosening, including the hips with a fractured stem, was present in 29.9 per cent. One additional revision, making ten in all, was done for symptomatic acetabular loosening. Based on this study, we concluded that conventional hip arthroplasty is a highly successful treatment in active patients between forty and sixty years old who have osteoarthritis of the hip.