A 25-year computerised survey of deaths in the United Kingdom among diabetic patients of 19 years of age and under was performed. Suitable pancreatic material was available in 119 out of the 498 identified patients. The duration of diabetes was known in 95 of the 119 patients. In 60 patients it had been present for less than 1 year. Insulitis was present in 47 of the 60 patients (78%) with recent onset disease, and was also found in 3 patients who had been treated for diabetes for between 1 and 6 years. In cases in which it was identified, insulitis affected 23% of islets containing insulin, but affected only 1% of islets which were insulin deficient, thus supporting the concept that insulitis represents an immunologically mediated destruction of insulin secreting B cells. Four patients appeared to have a different disease from classical Type 1 (insulin-dependent) diabetes in that there was no evidence of insulitis and all islets contained insulin. The age of onset of diabetes was eighteen months or less in these patients.