There has been described an operation for the conservative surgical treatment of benign giant-cell tumors in the distal end of the femur, in cases in which the articular cartilages of the knee joint are intact. This method permits removal of the tumor, and yet retains mobility of the knee joint and the full weight-bearing function of the leg. The procedure consists of obliterating the cavity by telescoping the fragments of bone, after removal of the tumor by curettage and chemical cauterization. To date the patients (all women) have accepted the shortening incurred, and have declined our offers to equalize length by operative shortening of the normal limb.