Aims: Uterine leiomyomas are the most common benign tumors of the uterus. Unfortunately, the diagnostic imaging criteria for distinguishing leiomyosarcomas from leiomyomas remain vague. Our aim was to study the preoperative diagnostic value of CA 125 in the differential diagnosis of leiomyoma and uterine sarcoma. Methods: The subjects of the study included a total of 2,382 patients aged between 20-71 years operated for uterine myoma between the years 2005 and 2008 at our hospital, and in the same period 26 patients diagnosed with uterine sarcoma who were assessed retrospectively. Results: Assessment of the predictivity of CA 125 values in the preoperative diagnosis of uterine sarcoma showed ıt was not significant according to the 95% CI related to the area below the curve. The assessment of CA 125 values in the uterine sarcoma group showed that those with carcinosarcoma had higher CA 125 mean values than other sarcoma groups. The relation between staging and CA 125 in all sarcomas could not be statistically assessed. Conclusion: We concluded that in the differential diagnosis of myoma and uterine sarcoma, the preoperative serum CA 125 level did not have any predictivity. Additionally, there was no association between staging and CA 125 in uterine sarcomas.