Ovarian cancer makes up 25–30% of all cases of cancers of the female genital tract. It has the highest mortality rate of any condition in oncological gynaecology. Early diagnosis is associated with a favourable 5-year survival prognosis. Many solid tumours have been detected with concomitant thrombocytosis. The tumour cell-induced platelet aggregation is a result of a direct integration of tumour cells with blood platelets. The aim of the present paper is an evaluation of platelet count as a prognostic parameter for ovarian cancer. Between 2000 – 2005, 349 patients with ovarian tumour (aged 12 – 88-years-old) underwent primary surgical treatment at a clinic. Ninety-seven patients with ovarian carcinomas underwent chemotherapy in the Oncology Centre. The control group comprised 252 women diagnosed with a histopathological lesion of mild intensity, whereas the cancer group constituted 97 women with a histopathologically-diagnosed malignant neoplasm. Thrombocytopaenia was assumed with a platelet count below 150G/L and thrombocythaemia at 350G/L and higher. Thrombocytosis often coincides with ascites and the cytoreduction decreases platelet count. There is a positive correlation between platelet count and tumour grading. Thrombocytosis was more frequently found in high grade tumours. There is also a positive correlation between platelet count and tumour stage according the International Federation of Gynaecology and Obstetrics (FIGO). Thrombocytosis was more frequently found in stage III and IV cancers. Patients with co-occurring thrombocytosis were found to have shorter survival periods and shorter time free from disease. This seems to give grounds for measuring platelet count before the primary surgical intervention, and suggests that the platelet count should be included in the panel of prognostic factors for patients with ovarian tumours.