In this study, we aimed to compare Cystatin C (Cys C) with other traditional glomerular filtration rate (GFR) markers and to evaluate its superiority over them in detecting early renal involvement in patients with primary hypertension. Fifty-one primary hypertensive patients and 29 healthy control subjects, who were similar in terms of age and gender, were included in the study. In all subjects serum levels of Cys C, beta-2 microglobulin, serum creatinine (SCr), uric acid, BUN, albumin; 24 h urinary levels of protein (Upro), albumin (Ualb) and creatinine were measured. The GFR was calculated according to Creatinine Clearance (CrCl), Cockcroft-Gault (CG) and Modification of Diet in Renal Disease (MDRD) formulas. The MDRD was used as the reference method. A GFR<80 mL/min/1.73 m2 was considered as the lower cut-off limit. Mean levels of the serum parameters were found to be significantly higher in the patient group than they were in the control group (p<0.05). Mean CrCl, CG, and MDRD levels were lower in patients than they were in controls but the difference was statistically significant for CG and MDRD. The serum parameter having the best correlation with MDRD was SCr (r = -0.760) in patients and Cys C (r = -0.622) in controls. However, in ROC analysis; the area under curve (AUC) for Cys C was found to be superior (AUC = 0.900) to the other markers. The CrCl was the parameter having the worst diagnostic efficiency (AUC = 0.598). As a conclusion, compared to other traditional markers, measurement of Cys C may be a better parameter to estimate GFR, especially to detect mild reductions of GFR in primary hypertensive patients.