In type 1 diabetes mellitus, islets are destroyed by the body's immune system. Clinical studies have shown that islet transplantation can support glucose homeostasis in type 1 diabetic patients and it carries the special advantages of being less invasive and resulting in fewer complications compared with pancreas transplantation. Islet transplantation shows short-term benefits of insulin independence, remarkable reductions in HbA(1c) levels, and elimination of severe hypoglycemic episodes. However, islet transplantation efforts have limitations such as the short supply of donor pancreata. The formation of new beta cells from stem/progenitor cells is an active area of investigation. Recent progress in the search for new sources of beta cells has opened up several possibilities for the development of new treatments for diabetes.