Previously, recurrence of insulin-dependent diabetes mellitus after pancreas transplants was only sporadically reported. Newer data, however, indicate recurrence rates as high as 5%. After identical-twin pancreas transplants, diabetes recurs in the absence of immunosuppressive therapy - strong evidence that it is an autoimmune disease. After deceased donor pancreas transplants, immunologic markers (autoantibodies, autoreactive T cells) herald recurrence. Selective destruction of β cells, still relatively uncommon, is not restricted to MHC compatibility. The development of diabetes in living pancreas donors is rare; it can be largely avoided by meticulous metabolic evaluation before donation and prevention of obesity after donation.