Eighteen children with pneumocystis carinii pneumonia diagnosed over a period of 16 years at a children's hospital are reviewed. All had an underlying disease, either congenital immunodeficiency or a malignancy. 15 patients were treated, 10 with pentamidine isethionate alone, 2 with both pentamidine and co-trimoxazole, and 3 with co-trimoxazole alone. 12 of the treated group recovered and the 3 untreated patients died. The 3 deaths after treatment occurred in children receiving pentamidine alone, and in whom secondary factors contributed. The side effects of treatment with pentamidine were high, and included local reactions, hypoglycaemia, and uraemia. However, our results confirm that pentamidine is an effective treatment for pneumocystis carinii pneumonia in childhood. Co-trimoxazole may be an effective and relatively nontoxic alternative treatment.