In this study; serum levels of different tumor markers such as alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), cancer antigen 125 (CA 125), cancer antigen 19-9 (CA 19-9), cancer antigen 15-3 (CA 15-3), and prostatespecific antigen (PSA) in 36 predialysis, 42 hemodialysis (HD), 42 continuous ambulatory peritoneal dialysis (CAPD) patients and 32 healthy volunteers as control group who did not present any clinical symptoms or signs of neoplasia with negative hepatitis markers were studied. The mean serum levels of CEA and CA 19-9 were found to be higher than the control group in predialysis, HD and CAPD patients. Serum levels of CA 125 in CAPD group was found to be higher as compared to the other groups. Serum AFP, CA 15-3 and PSA levels were similar in all groups. In conclusion, serum tumor markers do not have any diagnostic utility and may be unreliable for monitoring malignancies in uremic patients. [Turk J Cancer 2007;37(4):143-147]