The prevalence of spontaneous pneumothorax was studied in 82 patients with cryptogenic fibrosing alveolitis. In 46 patients the disease affected only the lung (‘lone’ fibrosing alveolitis); in the remaining 36 patients the interstitial lung disease was associated with several systemic diseases (‘associated’ fibrosing alveolitis). 3 patients with the ‘lone’ form had a spontaneous pneumothorax. This figure represents a prevalence of 3.6%. We did not observe this complication in any patient with the associated form. Suction drainage was ineffective in the 3 patients. One of them died as a consequence of pleural infection. In the other 2 subjects thoracotomy, resection of blebs and pleurectomy were required.