Insulin-dependent diabetes is the direct consequence of an autoimmune reaction causing the destruction of the beta cells of the islets of Langerhans in the pancreas. The frequent association of diabetes with other diseases involving the immune system, the detection of circulating antibodies aimed at the islet cells, the occurrence of the disease in subjects with peculiar HLA antigens are as many arguments supporting the immunological hypothesis. The study of animal models of insulin-dependent diabetes (BB rats, NOD mice) now allows demonstrating the autoimmune process. The transient effectiveness of cyclosporin demonstrated in the human disease confirms these data. The prospects of transplantation of the pancreas, of islets or of islet cells in diabetic subjects to compensate for the insulin deficiency therefore raises the double immunological problem of allogenic rejection and of the risk of recurrence of the anti-islet autoimmune disease.