Several studies carried out in a limited number of patients demonstrated a wide range of overestimation of glomerular filtration rate (GFR) by serum creatinine level and creatinine clearance (Ccr) in liver disease. We simultaneously evaluated Ccr, inulin clearance, and predicted GFR calculated from serum creatinine level in 56 cirrhotic patients. Inulin clearance was considered the gold standard for GFR evaluation. The sensitivity of serum creatinine level, predicted GFR, and Ccr in detecting renal failure was 18.5%, 51%, and 74%, respectively. On the basis of inulin clearance, patients were divided into two groups: those with normal GFR (mean, 106 +/- 34 mL/min per 1.73 m2) (group 1, 29 patients) and those with reduced GFR (mean, 56 +/- 19 mL/min per 1.73 m2) (group 2, 27 patients). Predicted GFR and Ccr were accurate markers of GFR in group 1 patients, while both overestimated GFR by about 50% in group 2 patients. An increased tubular secretion of creatinine accounted for the disparity between Ccr and inulin clearance in these patients. Our results indicate that renal failure is greatly underestimated on the basis of serum creatinine level and Ccr in cirrhotic patients. Clinical implications of this observation include excessive dosage of potentially nephrotoxic drugs and failure to recognize renal impairment induced by such medical treatments as diuretic therapy or paracentesis.