Objectives: The purpose of the study was the assessment of the helpfulness of Ca 125 serum level in preoperative staging of ovarian malignancies. Material and methods: The group of 224 ovarian cancer patients, diagnosed and treated surgically at Gynecological Ward of Municipal Hospital No 2 in Ruda Śląska. All patients were examined bimanually, the transvaginal ultrasound with Doppler microvessel density assessment of the tumor was performed and the serum Ca 125 level was estimated. The precise interview was done. The diagnosis was based on the histopathological examination of the operative specimens. The range of the serum marker level in the groups of malignant and benign masses was assessed. The sensitivity and the specificity of the above factor were counted in dependency on the cut-off value. The classification possibility was introduced using the ROC curve. Results: Among the analyzed group there were 193 benign lesions and 31 malignant tumors. The most frequent cut-off value in the literature 30 U/ml achieved sensitivity of 67.7% and specificity of 83.9%. The area under ROC curve was 0.807. Conclusions: The preoperative serum Ca 125 level assessment in the diagnosis of ovarian malignancies may be helpful, but not decisive.