To evaluate the effects of congenital diaphragmatic hernia (CDH) and pulmonary hypoplasia on subsequent lung function and development, we performed lung 133Xe ventilation and 99mTc perfusion scintigraphies in a group of infants who had undergone surgical repair of a severe left CDH with respiratory distress within the first 6 h of life. The initial lung scans performed in 15 children, 2-3 months of age, demonstrated a decreased ventilation in 7. In 9 children there was a trapping of 133Xe at the left lung base. Perfusion to the hernia side was reduced in 8 of the children. We re-evaluated 11 of these 15 patients after 1-2 years. The ventilation to the left lung was still decreased in 3, but perfusion remained decreased in 9. After 5 years, ventilation to the hernia side was normal in 4 of the 5 patients studied, whereas pulmonary blood flow was abnormal in 4. These results show a progressive improvement of ventilation with a persisting reduction of perfusion to the lung of the hernia side, suggesting a primary vascular pulmonary hypoplasia in CDH.