Posttransplantation diabetes mellitus (PTDM) is a well-recognized complication of renal transplantation. PTDM is reported to contribute to major infections and cardiovascular complications and leads to increased posttransplantation morbidity. The present study was conducted to evaluate the frequency of PTDM in our center, to identify the role of immunosuppressive therapy and other risk factors in the genesis of PTDM, and to assess the impact of PTDM on graft and patient survival. From December 1998 to December 2003 we followed-up 1200 renal transplant recipients, including 121 recipients with pretransplantation diabetes mellitus and 1079 recipients without diabetes. PTDM occurred in 203 patients (mean age, 35.4 +/- 5.9 years); 131 (64.5%) were male. Graft loss and mortality were significantly higher in patients with PTDM versus those without. The overall reported incidence of PTDM worldwide varies from 3.4% to 46%. The incidence in our center is 18.8%. We also found a significantly higher incidence of PTDM among patients receiving grafts from living-related donors. This may be related to the higher cumulative doses of immunosuppressive drugs administered (in part, due to the greater number of acute rejections) in these patients.