The pancreatic autopsy findings of 11 children with Type 1 (insulin-dependent) diabetes mellitus are presented. Nine children died within 24 h of initial presentation. In these 'recent-onset' diabetic patients many islets were shrunken and insulin-deficient. However, large islets containing B cells were present also. Insulitis was present in eight recent-onset diabetic subjects; in these, 18% of insulin-containing islets were inflamed, but only 1% of insulin-deficient islets were thus affected. This finding supports the concept of an immunologically mediated destruction of B cells in the pathogenesis of Type 1 diabetes. Severe acinar cell atrophy was present surrounding insulin-deficient islets, but acinar tissue around insulin-containing islets was normal. These exocrine changes are thought to be related to islet-exocrine vascular connections and the effects of the various islet hormones on pancreatic acini.