According to important role of post transplant DM (PTDM) and its complications and in prognosis of kidney transplantation, we tried to study the incidence of this problem and to determine its risk factors. The study included 50 patients of renal transplant candidates population between October 2004 and October 2005. Diabetes cases excluded. Pretransplant glucose tolerance test (GTT1) were performed and was repeated 2 months after transplantation (GTT2). Also existence of the following factors were evaluated: Body mass index hypertension, hyperlipidemia, history of DM in first degree relative and the form and duration of pretransplant dialysis. All patients received CSA and esteroid and MMF or Immuran after transplantation. 13 of 50 patients demonstrated hidden DM (26%) that were discovered by GTT1.6 patients developed new onset DM after transplant (16%). All of these had abnormal glucose tolerance befor transplant. Statistical analysis revealed significant relation between age and glucose tolerance test impairment (P=0.009). Also this problem was more prevalent in patients with longer duration of disease, history of DM in relative, hyperlipidemia and over or underweight, but statistical values were not significant. GTT is more sensitive than FBS in renal transplant candidate as a screen test. Many factors such as age, malnutrition, hyperlipidemia, history of DM in relative and obesity increase the risk of PTDM.