The effect of muscle-sparing versus standard posterolateral thoracotomy on pulmonary function, muscle strength, and postoperative pain. Increased interest in alternative approaches to thoracotomy has developed because of the considerable morbidity associated with the standard posterolateral technique. We conducted a prospective, randomized, blinded study of 50 consecutive patients to compare postoperative pain, pulmonary function, shoulder strength, and range of shoulder motion between the standard posterolateral and the muscle sparing thoracotomy techniques. Pulmonary function (forced expiratory volume in 1 second and forced vital capacity), shoulder strength, and range of motion were measured preoperatively and at 1 week and 1 month postoperatively. Pain was quantitated by postoperative narcotic requirements, the visual analogue scale, and the McGill pain questionnaire. Morbidity, mortality, and hospital stay were compared between the standard posterolateral and muscle-sparing techniques. There were no differences in postoperative pulmonary function, shoulder range of motion, extent of lung resection, surgical approach time, mortality, or hospital stay. There was significantly less postoperative pain in the muscle-sparing group. The narcotic requirement was less in the first 24 hours (p = 0.0169), and visual analogue scale scores were significantly lower (p less than 0.05) throughout the first postoperative week. Shoulder girdle strength was decreased at 1 week in the standard incision group whereas the strength was preserved with the muscle-sparing approach. Muscle strength had returned to preoperative levels by 1 month in both groups. Morbidity was identical in the two groups with the exception of postoperative seromas. The prevalence of seroma was 23% in the muscle-sparing group and 0% in the standard incision group (p = 0.0125). We have demonstrated that the muscle-sparing incision may be a reasonable alternative to the standard posterolateral approach. 