Islet transplantation is the transplantation of isolated islets from a donor pancreas into another person. It is an experimental treatment for type 1 diabetes mellitus. Once transplanted, the islets begin to produce insulin, actively regulating the level of glucose in the blood.

Islets are usually infused into the person's liver. If the cells are not from a genetically identical donor the person's body will recognize them as foreign and the immune system will begin to attack them as with any transplant rejection. To prevent this immunosuppressant drugs are used. A study from 2005 showed that islet transplantation has progressed to the point that 58% of the people were insulin independent one year after the operation. A review published 2016 reported a 50 – 70% rate of insulin independence after five years, in five studies from leading transplant centers published 2005 – 2012.

In the period from 1999 to 2004, 471 people with type 1 diabetes received islet transplants at 43 institutions worldwide.