We sought to determine the risk factors involved in the development of posttransplantation diabetes mellitus (PTDM) following simultaneous pancreas and kidney transplantation. Correlations were sought between tacrolimus (FK-506) levels/dose 2-hour capillary glucose (CG) and glycosylated hemoglobin (HbA(1c)), cyclosporine (CSA) levels/dose with HbA1c, 2-hour CG with prednisone dose and body mass index (BMI) and PTDM. Four patients (9.3%) developed PTDM. Three treated with FK-506 had altered 2-hour CG at 3 months after transplantation; 1 prescribed CSA displayed diabetes diagnosed after 1 year. There was no statistically significant difference among HbA(1c) values and FK-506 (P =.18) or CSA (P =.81) doses or FK-506 (P =.53) and CSA (P =.54) levels. In contrast, there was a statistically significant relationship between elevated 2-hour CG (> or =200 mg/dL) and daily prednisone dose (9.7 mg vs. 16.2 mg; P =.003). There was no correlation between 2-hour CG and FK-506 dose (P =.084) or FK-506 levels (P =.075). The greater BMI correlated with an increased risk of PTDM (21.25 +/- 3.13 kg/m(2) vs 24.67 +/- 2.38 kg/m(2); P =.034). Two-hour CG may be a useful tool to screen the diabetogenic effects of corticosteroids. A BMI increase should be discouraged due to the risk of PTDM.