Insulin dependent diabetes mellitus ranks as one of the major disease entities in the world. It is widespread in industrialized countries as well as in developing countries. In spite of the considerable improvements in conventional diabetes therapy during the past few years, severe secondary complications still develop in most patients. The National Commission on Diabetes in the United States has reported that patients with insulin dependent diabetes are 25 times more prone to blindness, 17 times more prone to kidney disease, 5 times more often afflicted with gangrene and twice as often afflicted with heart disease than are non-diabetic individuals. In Sweden diabetes is now the second most common cause of uremia and it is the most common cause of blindness in adults. The life expectancy for the diabetic patient is approximately one-third less than that of the general population. Since the metabolic abnormalities that prevail in diabetes mellitus are due to abolished beta-cell function, it would seem logical to treat this disease by the transplantation of normally functioning islets of Langerhans. This operation should correct the metabolic abnormalities and presumably prevent or delay the severe secondary complications. There are two ways of transplanting the endocrine pancreas, either by means of a vascularized graft or by providing free, isolated islets. Unfortunately it has not been possible, so far, to correct diabetes in humans with islet transplantation. However, during the last years there has been substantial progress in the field of vascularized pancreatic transplantation and the results now begin to approach those obtained with other organs such as the kidney, heart, and liver.