Long-standing type 1 diabetes (T1D) is associated with an absolute loss of endogenous insulin secretion (circulating C-peptide is undetectable) and a related defect in glucose counter-regulation that is often complicated by hypoglycemia unawareness, markedly increasing the risk for severe hypoglycemia. Both the transplantation of isolated islets and a whole pancreas can restore β-cell secretory capacity, improve glucose counter-regulation, and return hypoglycemia awareness, thus alleviating severe hypoglycemia. The transplantation of islets may require more than one donor pancreas, and the recovery of endocrine function for now appears more durable with a whole pancreas; however, islet transplantation outcomes are steadily improving. Because not all patients with T1D experiencing severe hypoglycemia are candidates to receive a whole pancreas, and since not all pancreata are technically suitable for whole organ transplantation, islet and pancreas transplantation are evolving as complementary approaches for the recovery of endocrine function in patients with the most problematic T1D.