Objective: To evaluate the usefulness of the platelet count and CA-125 in the discrimination between malignant and bening ovarian tumors at the Hospital Universitario de Los Andes, in a period of 5 years. Methods: Retrospective observational research. 419 patient medical stories coded as ovarian tumors were reviewed. The definitive pathology report was used as the gold standard test. Multiple statistical parameters of diagnostic performance were calculated from 2x2 tables and receiver operating characteristic (ROC) curves were plotted. Results: The mean platelet count: with invasive malignant ovarian tumors was 386/nl (CI 95 % 362-409), in benign tumors it 243/nl (CI 95 % 235-251) and in borderline tumors 237/nl (CI 95 % 198-276). Although the area under the curve receiver operating characteristic was higher for platelet count compared to CA125 levels (0.880 vs 0.790) this difference was not statistically significant. Among the mucinous tumors, the malignant ones did not present an elevated CA-125, but an elevated platelet count. Highest PPV of the platelet count was 95.6 % for > 350 / nl in postmenopausal women and 100 % for > 400/nl (p <0.001). Conclusion: The platelet count seems to have a similar utility to CA-125 to discriminate malignant from benign tumors and could improve diagnostic performance when both preoperative values are combined. Keywords: Platelets, Thrombocytosis, Ovary, Tumor, Cancer, CA-125, Diagnostic accuracy, Menopause.