Post-transplantation diabetes mellitus (PTDM) develops in 10-15 % of all renal transplant recipients within 10 weeks after transplantation, and has been associated with increased risk of cardiovascular disease and impaired patient survival. PTDM is primarily believed to be a variant of type 2 diabetes mellitus (T2DM), but the pathophysiology underlying the impaired glucose metabolism in renal transplant recipients with PTDM is unclear and some aspects are still poorly investigated. Hyperglycemic clamp investigations with concomitant infusion of glucagon-like peptide-1 (GLP-1) are warranted for a thorough characterization of the α-cell and β-cell function.