An analysis of the efficacy of two techniques of posterior spinal instrumentation in patients with idiopathic scoliosis was performed. Thirty-two consecutive patients treated with Cotrel-Dubousset instrumentation and no external bracing were compared with 30 consecutive patients treated with Harrington rod instrumentation supplemented by Bobechko hooks, sublaminar wires, and postoperative bracing. The groups were similar in age, curve magnitude, and type. Cotrel-Dubousset instrumentation demonstrated significantly improved immediate frontal plane correction. It was also more effective in improving thoracic kyphosis, particularly in patients with preoperative hypokyphosis. Both procedures were performed with similar operative time, blood loss, and minimal complication rates.