The final diagnosis of ovarian cancer is based on surgery and pathological verification. Therefore patients who are presented to surgery may be described only as supposed ovarian cancer. According to the literature the diagnosis of ovarian cancer is confirmed only in 2/3 of them. The rest are that which mimic ovarian cancer. One of them is colorectal cancer. Colonoscopy is a gold standard in its diagnostics. On the other hand, ovarian cancer may disturb the bowel patency and makes the bowel resection or stoma necessary.The main aim was to find out the distribution of bowel patency disturbances in ovarian cancer patients during preoperative colonoscopy and to assess their predictive value with respect to the bowel resection or stoma and the additional aim to identify the pathologies which mimic the ovarian cancer.In a prospective study among 104 patients with supposed ovarian cancer, primary ovarian cancer was diagnosed in 68 patients. The rest of them suffered from colorectal cancer found at colonoscopy (N = 6), ovarian benign pathology (N = 8), ovarian borderline tumor (N = 5), and other nonandexal malignant diseases (N = 17). In ovarian cancer group dominated serous carcinoma and fedération international de gynécologie et d'obstétrique stage 3 (N = 33).During preoperative colonoscopy in ovarian cancer patients, the complete obstruction was found in 27.9%, and relative risk of bowel resection or stoma was in them 4.29 and 4.38, respectively. Another colonoscopic finding was limited patency caused by extrinsic compression (29%) which is connected with relative risk of bowel resection or stoma 3.16 and 3.21 accordingly. The last colonoscopy finding was described as moderate limited patency of unknown origin (20.6%) and the relative risk of bowel resection or stoma was 5.14 and 4.17, respectively.Colonoscopy enables the diagnoses of colorectal cancer one of the diseases which mimic ovarian cancer in patients supposed to have this diseases.Bowel patency disturbances found at colonoscopy are a potential risk factor to intestine resection or ostomy.Colonoscopy is not fully noninvasive procedure and its obligatory use in patients supposed to have ovarian cancer should be limited to the cases with specific symptoms, and tumor marker pattern. Preoperative computed tomography, dedicated to bowel examination, candidates as an alternative to colonoscopy, but not completely.