STUDY DESIGN: Retrospective chart review. OBJECTIVES: To investigate the role of plasma creatinine (p-creatinine) in monitoring renal deterioration in patients up to 50 years after spinal cord injury (SCI). SETTING: The Clinic for Spinal Cord Injuries, Rigshospitalet, Denmark. METHODS: A total of 119 patients with a traumatic SCI during the years 1944-1975 were included in the study. P-creatinine measurements, results from renography and glomerular filtration rate (GFR) measured with 51Cr-EDTA clearance were obtained from medical records and analyzed using a linear mixed model and linear regression analyses. RESULTS: When compared with median p-creatinine level in the first 5-year period after injury, the level of p-creatinine was stable throughout the first 30 years and decreased significantly after the 30th until 45th year post injury. Only patients with a functional distribution outside the 30-70% limits on renography or a relative GFR < or =51% of that expected had a significantly elevated level of p-creatinine. Significance was not found for patients with a distribution outside the 40-60% limits on renography or relative GFR < or =75%. By comparing Cr-EDTA clearance and p-creatinine in terms of exceeding the upper reference level, p-creatinine revealed 17% sensitivity, 100% specificity, 100% positive predictive value and 73% negative predictive value as a diagnostic test for renal deterioration defined as GFR < or =75%. CONCLUSION: P-creatinine decreases over time in patients with SCI with a level below the upper reference limit and is a poor detector of early renal deterioration in patients with SCI.