OBJECTIVE: The resistance of blood to flow is called plasma viscosity. Increased blood viscosity has been described in patients with coronary and peripheral arterial disease. In this study, we evaluated the influence of clinical and laboratory findings on plasma viscosity in renal transplant recipients. METHODS: Eighty-one kidney transplant recipients (37.8 ± 11.3 years old, 50.38 ± 16.8 months post-transplantation period, 27 female) with normal graft functions were enrolled. The biochemical and clinical parameters in the 1st year after transplantation were retrospectively recorded, and graft function was evaluated by means of the yearly decline in eGFR. Plasma viscosity was measured and searched for the association with cross-sectionally analyzed cardiovascular parameters including body composition analyses, ambulatory blood pressure monitoring (ABPM) data, and pulse-wave velocity. RESULTS: Patients were divided into 2 groups according to the median value of serum viscosity. Patients with high viscosity had higher serum low-density lipoprotein (P = .042) and C-reactive protein (P = .046) levels than lower viscosity group. In ABPM, daytime (P = .047) and office systolic (P = .046) blood pressure levels and left ventricular mass index (LVMI; P = .012) were significantly higher in patients with hyperviscosity. Patients with high viscosity had higher hip circumference (P = .038) and fat mass (P = .048). Estimated glomerular filtration rate decline was significantly higher in high-viscosity patients than in patients with low viscosity levels (12.9% vs 17.2%; P = .001) at 2 years' follow-up. CONCLUSIONS: We suggest that the hyperviscous state of the renal transplant recipients may arise from the inflammatory state, hypertension, and increased fat mass and increased LVMI. Hyperviscosity is also closely related to renal allograft dysfunction.