The aim of this prospective study was to determine the rate of recurrence for spontaneous pneumothorax (SP) after tetracycline pleurodesis (TCP), using that of observation, tube thoracostomy alone, and thoracotomy as references. From 1985 to the end of 1991, 78 patients were treated with tetracycline pleurodesis and 135 patients served as control subjects. Pleurodesis was induced by instillation of tetracycline and ascorbic acid through the pleural drain. The indication was any SP treated with tube thoracostomy, without active pulmonary infection. Follow-up period was from 13 to 95 months (mean, 45 months); follow-up rate was 94 percent. Post-therapy surgery was necessary for eight patients in whom pleurodesis failed due to presence of a persistent air leak. The ipsilateral recurrence rate of patients treated with TCP was 9 percent (6/66) and recurrence time ranged from 2 days to 9 months. The recurrence rate for patients treated with observation was 36 percent, 35 percent for those having chest tube alone, and none for those undergoing surgery. No death occurred as a direct result of this procedure and all patients could be released from the hospital. Eleven subjects died during the follow-up period; the mean follow-up until death was 37 months (range, 2 to 87 months). Five deaths were due to respiratory causes and six were due to extrapulmonary causes. Tetracycline pleurodesis has been shown to be a good alternative for the prevention of recurrence of SP. Its recurrence rate is lower than that of tube drainage but higher than that of surgical treatment.