An investigation was carried out of 821 children under the age of 16 years who were subjected to splenectomy in England and Wales during the 5 years 1960-4. A postal follow-up study provided satisfactory information concerning 96 per cent of these. Excluding early postoperative deaths, practically all the cases were followed up for 2 years or more and 70 per cent for more than 5 years. Forty-nine children had died since operation, 32 from underlying disease and 17 from infection. Fifty children (6 per cent of the survivors) had major infections considered to be due to the primary condition aggravated by splenectomy. Seven died, all from the primary disease. Sixteen children (2 per cent) developed septicaemic illnesses and 10 died. In these the effect of splenectomy was considered to be the primary factor. Fourteen of the 16 had been operated on in the first 4 years of life. Practically all the serious infections occurred within 3 years of operation and pneumococcus was the organism most frequently implicated. Ninety per cent of the splenectomies in childhood were performed for accidental injury, congenital haemolytic anaemia or idiopathic thrombocytopenic purpura. Accidental injury to the spleen rarely occurs in very young children, and in the other two conditions splenectomy can usually be safely delayed untile over the age of 3 years. If this is achieved it is estimated that the unavoidable risk of dangerous infection is less than 1 per cent. One in 10 splenectomies will be carried out for severe and potentially fatal illnesses and in this situation the risk from operation is of secondary importance. Many such conditions carry increased susceptibility to infection per se or because corticosteroids or other immune suppressants are used in their management. It is recommended that splenectomy be avoided if at all possible during the early years of life. It is further recommended that prophylactic penicillin be administered for 3 years following operation whatever its indication and whatever the age of the patient. If the underlying condition itself carries risk of infection more active and more prolonged prophylaxis may be indicated.