Fifty-eight patients who had scoliosis or kyphosis of varying etiologies were followed for a minimum of two years (average, forty-four months) after segmental spinal instrumentation using sublaminar wires. In eight (19 per cent) of the patients who had been operated on for scoliosis one or both rods broke. The average time that had elapsed before the breakage was discovered was twenty-three months. None of the patients in whom a rod had broken had had postoperative immobilization or a first-stage anterior fusion, and only one had had supplementary grafting with banked bone. Instrumentation to the pelvis was also associated with a greater incidence of broken rods. The use of supplementary grafting with banked bone or the use of postoperative immobilization significantly decreased the loss of postoperative correction. Preliminary anterior spinal fusion helped prevent breakage of rods but not loss of correction. It was concluded that postoperative immobilization and use of large amounts of supplementary bone graft lead to better results when using this implant system.