The availability of new immunosuppressive drugs has led to improvement in outcome for transplanted patients, but these drugs have also led to the increase of metabolic abnormalities, such as dyslipidemia and hyperglycemia, which can affect graft and patient outcome. Posttransplant diabetes mellitus (PTDM) or new-onset diabetes after transplantation is defined as the onset of diabetes in previously nondiabetic transplant recipients. Several clinical studies have demonstrated the involvement of PTDM in death due to infectious and cardiovascular disease. This article reviews recent concepts on pathophysiology, diagnosis, and treatment of PTDM.