The incidence of pulmonary barotrauma during mechanical ventilation in children beyond the neonatal age group was studied in two groups of patients. In the first group, 179 cases of pediatric mechanical ventilation for over 12 hours were retrospectively analyzed for the occurrence of pneumothorax and pneumomediastrinum. Eleven percent (6 of 57) of young infants (0--6 months) without hyaline membrane disease and 3% (4 of 122) of older infants and children (over 6 months) developed these complications. Pulmonary barotrauma in young infants occurred only after cardiothoracic surgery and involved the same site as the intraoperative repair in all cases. Pulmonary barotrauma in older infants and children occurred in patients with severe respiratory disease requiring high peak airway pressures, PEEP, and respiratory rates. In the second group, the incidence of pulmonary barotrauma during ventilation with PEEP greater than or equal to 15 cm H2O was analyzed in 14 patients including 4 patients from the previous group. Overall, 64% (9 of 14) of this group developed pulmonary barotrauma and 43% (6 of 14) developed pneumothorax. Of 9 patients receiving PEEP greater than or equal to 15 cm H2O for longer than 24 hours, 6 developed pulmonary barotrauma after the first 24 hours. The incidence of pneumothorax and pneumomediastinum in ventilated infants without hyaline membrane disease and children is comparable to adult series.