Objective: To investigate the relationship between serum cystatin C, serum creatinine, and 51 Cr-EDTA-clearance in patients with spinal cord injury. Setting: The Spinal Cord Unit, Viborg-Kjellerup County Hospital. Methods: Twenty-four men and seven women aged 20.3 to 68.0 years with motor complete spinal cord injury (ASIA A or B) were included. Serum cystatin C was measured by an automated particle-enhanced nephelometric immunoassay (Dade Behring), serum creatinine by an enzymatic method (Vitros 950), and 51 Cr-EDTA-clearance by a multiple plasma sample method. Results: A linear relationship was found between 51 Cr-EDTA-clearance and the reciprocal values of cystatin C and creatinine. The correlation coe cient between 51 Cr-EDTA-clearance and 1/cystatin C was 0.72 compared to the correlation coe cient between 51 Cr-EDTAclearance and 1/creatinine being 0.26. Comparison of the area under the curves in the nonparametric receiver operating characteristics (ROC) plots for serum cystatin C (area under the curve (AUC)=0.912; SE=0.065), and serum creatinine (AUC=0.507; SE=0.115) revealed signi®cant di erences (P-values=0.0005). Conclusion: In patients with spinal cord injury serum cystatin C is a better marker of the renal function compared to serum creatinine.