The results of open thoractomy and pleurectomy or pleural abrasion for 17 episodes of pneumothorax in patients with cystic fibrosis were compared with the results of observation, closed thoracostomy, and closed thoracostomy with sclerosing agents. Open thoracotomy had the advantage of insuring prompt resolution of the pneumothorax. A small incision minimized postoperative morbidity. The average hospital stay was 15 days after open thoracotomy and 19 days after closed thoracostomy, with or without sclerosing agents. Complications of all treatments were infrequent. A limited symptomatic recurrence was observed in 2 of 17 pneumothoraces successfully treated with open thoracotomy. Recurrence also occurred in 1 of 8 treated with observation, 3 of 9 treated with closed thoracostomy, and 1 of 14 treated with closed thoracostomy and sclerosing agents. A loss of vital capacity was usually noted 4 to 18 months after resolution, regardless of treatment. Forty per cent of patients in both operative and nonoperative groups survived 3 years. In our experience, open thoracotomy can be used safely for treatment of unresolved or recurrent pneumothorax and warrants further evaluation as a primary therapy for pneumothorax in patients with cystic fibrosis.