Twenty-one of 146 cases of spontaneous pneumothorax that were treated by thoracentesis or continuous low negative pressure suction drainage (-12 cm H2O) of the pleural space developed REPE. The rate of REPE was higher in patients 20 to 39 years of age than in those over the age of 40, and the rate progressively increased in proportion to the extent of pneumothorax, as assessed by roentgenographic criteria. It is postulated that age-related changes in the lung may afford some degree of protection against developing REPE. It is also suggested that the treatment of pneumothorax with thoracentesis and/or suction drainage in young patients, or in the face of a large pneumothorax, requires careful consideration in view of a relatively high incidence of REPE in such individuals.