Background: Cancer antigen 125 (CA-125) is a tumor marker used for the diagnosis and monitoring of ovarian carcinoma. It can also be elevated in endometriosis, inflammations, and in nongynecological malignancies. Up to date, serum CA-125 levels in inflammatory bowel diseases (IBD) have not been studied before. Aim: To assess the levels of CA-125 in patients with ulcerative colitis (UC) and Crohn's disease (CD). Methods: Serum levels of CA-125 were investigated in 68 cases with UC (male/ female: 47/21), 32 CD (male/female: 21/11), and 31 healthy controls (male/female: 16/15). Levels of CA-125 were also compared among UC patients according to lesion location, severity, and activity of CD. Results: Serum CA-125 levels were 17.29724.50 U/ml, 15.56720.74 U/ml, and 8.8572.62 U/ml in patients with UC, CD, and healthy controls, respectively. Serum CA-125 levels were significantly higher in UC compared to control group (P 5 0.001). Serum CA-125 levels were higher in CD patients compared to control group but there was no significance (P 5 0.087). Serum CA-125 levels were higher in pancolitis compared to distal type and left-sided UC. Conclusions: Our data suggest that serum CA-125 levels may be increased in patients with IBDs.