A long-term follow-up was carried out on 30 patients who had congenital diaphragmatic hernias operated on over a 21-yr period. The review took the form of clinical examination, chest x-rays, pulmonary function tests, and lung scans. Lungs that were hypoplastic at birth remained underdeveloped as judged by pulmonary function tests and hypoperfusion on lung scan; however, children who survived birth6 and operative repair went on to live normal lives through the period studied. There was some suggestion from pulmonary function tests and lung scans that in the older group a preemphysematous state may exist but this was asymptomatic. There was no evidence of increased susceptibility to respiratory infection in the group. Ten per cent of the children were mentally retarded, evidently from hypoxia after birth.