Objective: There are some data regarding the role of cystatin C, a cysteine proteinase inhibitor, in determining the glomerular filtration rate (GFR) more accurately. We aimed to evaluate the correlation of serum cystatin C levels with the serum creatinine levels and GFR calculated by Cockcroft-Gault and modification of diet in renal disease (MDRD) formulations in the patients who received cisplatin-based chemotherapy. We also intended to demonstrate its potential use in the early prediction of the renal function changes in these patients. Materials and methods: In the study, 34 patients receiving cisplatin-based chemotherapy with various malignancies were included. The levels of cisplatin were determined prior to the chemotherapy and at the end of cisplatin infusion during the therapy. GFR was calculated by Cockcroft-Gault and MDRD formulations prior to the therapy and at the end of the third course. Results: A statistically significant linear correlation was found between the serum levels of cystatin C and creatinine prior to the chemotherapy (r - 0.42, p - 0.013). However, there was no correlation among the level of cystatin C subsequent to the cisplatin infusion and serum creatinine level following the third course and MDRD and creatinine clearance-Cockcroft-Gault formulations. Conclusion: Even though the serum cystatin C levels were correlated with the serum creatinine levels in our study, it was concluded that it was not an appropriate parameter to predict the potential impairments in the renal function during the chemotherapy.