Prophylactic intramedullary nailing was performed in eighteen femora of fourteen patients who had neoplastic lesions in the femur and survived for from thirty-eight to 1309 days after nailing. The procedure enabled all but three patients to be ambulatory with a walker by four days after operation and to continue to walk until they became moribund shortly before death. The complications were: one postoperative infection, penetration of the nail through the femoral cortex in three femora before prebending of the nail became part of the procedure, and ectopic bone about the proximal end of the rod. The procedure is recommended for the prevention of pathological fracture and relief of pain.