We reviewed the records of all patients with cystic fibrosis and radiologically demonstrated pneumothorax at Rainbow Babies and Childrens Hospital between 1959 and 1987. There occurred 144 pneumothoraces, 71 right and 73 left, in 99 patients, 48 female and 51 male. The median survival from the date of the first pneumothorax was 29.9 months. Primary therapy included the following: observation; tube thoracostomy; tube thoracostomy with instillation of quinacrine hydrochloride, tetracycline, silver nitrate, or talc; or partial pleurectomy. Complications were minimal in each group. The surgical group did significantly better than all other groups except the group given talc. We conclude that pneumothorax is a late and ominous complication of cystic fibrosis. The primary treatment of pneumothorax should be partial pleurectomy. Talc instillation should be reserved for patients in respiratory failure who are too ill to undergo operation and for the occasional patient in whom surgical intervention fails.