The realization that Type I diabetes is an autoimmune disease and, in particular, a chronic autoimmune disease is beginning to impact on clinical care and research directed at elucidating the cause and prevention of diabetes. For example, specialized laboratory evaluation can now be used to exclude potential renal donors who are at high risk of developing diabetes (by screening renal donor candidates who are relatives of Type 1 diabetics for cytoplasmic islet cell antibodies and evaluating first phase insulin secretion on intravenous glucose tolerance testing). The most important long-term consequence of the ability to predict Type 1 diabetes may be the development of effective immunotherapy to prevent the disease. Finally, the realization that Type 1 diabetes is an auto-immune disease and that some of the antigens expressed by islets (e.g., specific gangliosides identified with monoclonal antibodies) are expressed by renal glomerular cells, retinal microvascular pericytes, and neurons has renewed interest in searching for immunologic factors contributing to secondary complications.