The only known cure for insulin-dependent diabetes mellitus is transplantation of functioning islet cells, either alone or via transplantation of the entire pancreas in sufficient mass to restore normal carbohydrate metabolism. Such therapy may also ameliorate or eliminate certain long-term consequences of diabetes. More than 3,000 patients have received pancreas transplants at 150 centers worldwide since 1966. Urinary drainage of pancreatic exocrine secretions has dramatically improved long-term survival, especially when a kidney was transplanted at the same time. Metabolic control then resumes normal function for up to six years, in some cases preventing or reversing long-term complications of diabetes. While nephropathy and neuropathy can be prevented and even somewhat reversed, retinopathy and neuropathy resist improvement. The large number of islets that must be harvested makes islet cell transplantation difficult to achieve, although the process has been accomplished in humans with limited success.