This study is carried out to evaluate the advantage of serum cystatine C as a marker of renal dysfunction over the routine renal function tests in cirrhotic patients and whether it has a correlation with degree of liver affection, while using Pugh's modification of child's classification as a marker of degree of liver affection. The result of this study showed and confirmed that in patients with cirrhosis, particularly in patients with Child-Pugh class C, cystatin C determination is a valuable tool for the diagnosis of moderately impaired renal function.