The aim of this study is to investigate the effects of ascites, ovarian mass volume, and peritoneal carcinomatosis on serum CA125 levels in patients with nonmucinous epithelial ovarian carcinoma. Serum CA125 levels were determined by a commercial enzyme immunoassay kit in a series of 98 patients with stage I-IV nonmucinous epithelial ovarian carcinoma. Amounts of ascites were determined in each patient with ascites. Ovarian mass volumes were calculated in 22 patients with stage I disease without ascites. Peritoneal carcinomatosis was detected in 35 ovarian cancer patients. Serum CA125 levels were compared among the patients with different clinical conditions. Serum CA125 levels were significantly higher in cases of ovarian cancer with ascites when compared with those without ascites (P < 0.01). Abnormal levels of serum CA125 were found in 80% of all patients; these abnormal levels were detected in 92% and 97% of the patients with ascites and with peritoneal carcinomatosis, respectively. A positive correlation between serum CA125 levels and ascites amounts was found in patients with ascites (P < 0.01, r = 0.74). However, there was no correlation between ovarian mass volumes and levels of serum CA125 in patients having stage I disease but no ascites (P = 0.5, r = 0.15). Our results showed that serum CA125 levels might be affected by the amount of ascites and the presence of peritoneal carcinomatosis but not with ovarian mass volume. However, these findings need to be confirmed in more and larger studies. These results may be beneficial in the management of ovarian carcinoma patients with elevated CA125 levels.