Background/aims: Cancer antigen 125 is a glycoprotein of 220 kDA molecular weight, that is released from coelomic epithelium during embryonic development. It has a low specificity, and high levels have been shown in many benign and malignant diseases. High correlation was detected between its level and ascites, especially in cirrhotic patients. In this study, we aimed to evaluate cancer antigen 125 levels in patients with ascites and determine the relationship between these levels and the amount of ascites. Methods: Fifty-eight patients (25 men, 33 women, mean age 54.34 years) with ascites, hospitalized in our clinic, were included in the study. The patients with ovarian cancer were not included. For all patients, physical examination and abdominal USG were done and blood samples for routine screening and cancer antigen 125 were obtained and studied on the same day. Results: Mean cancer antigen 125 levels in all patients were higher than normal. The highest levels were detected in patients with massive ascites and cirrhosis. With regard to diagnosis, the levels of cancer antigen 125 between groups were insignificant. According to USG results, there was a weakly positive but important correlation between groups. Although no correlation was present between cancer antigen 125 and ALT levels, a weak but positive correlation was present with AST levels. Conclusion: Our study showed that a correlation is present between cancer antigen 125 levels and the presence and amount of ascites. We also suggest that if cancer antigen 125 levels are above normal, the presence of ascites not detected by physical examination should be kept in mind.