Diabetes mellitus is a serious problem in patients after organ transplantation. It is an important risk factor of cardiovascular diseases, impairs graft function and shortens its survival. Diabetes mellitus after organ transplantation can be classified as pretransplant (being often the reason for transplantation) and posttransplant diabetes. Corticosteroids play an important role in development of the latter; therefore the lowest effective doses of them or alternative immunosuppressive drugs should be recommended. Patients with diabetes mellitus after transplantation should be treated according to general rules of treatment of this disease.