The records of 174 consecutive patients with congenital diaphragmatic hernia were reviewed to analyse the changes in the presentation, treatment and outcome during the 45-year interval from 1948 to 1992. For comparison the period was divided into years 1948-1962, 1963-1972, 1973-1982 and years 1983-1992. The proportion of high-risk cases (symptomatic within 6 h of birth) increased from 50 per cent during the first period to 77 per cent during the second, to 86 per cent during the third and to 94 per cent during the fourth. The primary mortality rate (death within 30 days of diaphragmatic repair) increased from 25 per cent during the first period to 35 per cent during the second, 46 per cent during the third and 49 per cent during the fourth. No change occurred in the proportion of infants with diaphragmatic hernia who were stillborn or who died in the maternity unit. Post-mortem lung weight was available in 56 children. Severe pulmonary hypoplasia correlated with early postoperative death and clinical severity. The mean(s.d.) lung weight ratio (combined lung weight divided by the lung weight expected for the body-weight) decreased from 0.70(0.49) during the second period to 0.56(0.36) during the third and 0.40(0.18) during the fourth. The increased proportion of more severe cases with very hypoplastic lungs explains the rise in the mortality rate of patients operated on for congenital diaphragmatic hernia. This may reflect a real change in the disease spectrum rather than improved referral.