Since renal failure causes decrease in tumor marker excretion, use of these markers in cancer care and treatment in patients with renal insufficiency or hemodialysis is controversial. The aim of this study was to investigate differences of serum levels of tumor markers CA15-3, AFP, CA19-9 and CEA in patients with impaired renal function. A total of 100 patients referred to the Tabriz Immam Reza and Amiralmomenin hospital from June 2010 to November 2011 were selected for study. Subjects were divided to 3 groups of healthy, dialysis and renal failure but non hemodialysis cases, the last category being re-grouped based on creatinine clearance. No significant relationship between different groups in serum levels of CEA (P=0.99) and CA19-9 (P=0.29) tumor markers was found. A significant correlation was observed between serum levels of AFP (P<0.001) and CA15-3 (P<0.001) and also a tendency between creatinine clearance and CEA (r=0.05, P=0.625). Creatinine clearance significantly correlated with AFP (P<0.001, r=0.53) and CA15-3 (p=0.00, r=-0.412), but not CA19-9 (P=0.089, r=-0.171). According to results of this study it appears that use of tumor markers in patients with impaired renal function should be performed with special precautions.