BACKGROUND Neopterin is a pyrazino-pyrimidine compound which is used as a marker of cell-mediated immunity in a variety of diseases. It is known that neopterin levels increase in diseases where interferon-gamma (IFN-g) stimulation is present, and also as a result of deficiencies in renal function, given that the primary means of elimination of neopterin is through the kidneys. In this study, we aimed to investigate the role of increased neopterin levels as a prognostic biomarker in patients with impaired renal function. METHODS A total of 90 individuals including 63 patients with chronic kidney failure (CKF) and 27 healthy volunteers were included in the study. Serum neopterin concentrations were measured using the enzyme-linked immunosorbent assay. A Mann-Whitney U test and a Pearson Correlation Test were used in the statistical analysis, with a p value of <0.05 being considered statistically significant. RESULTS The mean age was 52.21±0.16 years in the patient group and 56.55±0.32 years in the control group. In the CKF patients, serum neopterin levels increased to a significantly greater degree than in the control group (p<0.001), while no statistically significant correlation was identified between serum neopterin levels and age (p>0.05). CONCLUSIONS A significant increase was found in the serum neopterin levels in the CKF patients, due to both the triggering of the disease and the reduction of neopterin elimination.