The aim of this work was to compare mean concentrations of gonadotropins in serum and fluid from malignant and benign ovarian tumors. We enrolled 126 patients diagnosed with malignant epithelial tumors (n=40), borderline epithelial tumors (n ¼ 14), benign cystadenomas (n ¼ 28) and simple cysts (n ¼ 44) of the ovary. Premenopausal and postmenopausal subgroups were formed in each group. The concentration of FSH and LH was measured in serum and tumor fluid and the serum/tumor fluid ratio was calculated. The results in each group were compared and the sensitivity, specificity, positive and negative predictive values were determined.Mean concentrations of both gonadotropins in ovarian cancer fluid were significantly higher than in the remaining groups (P ranged from <0.005 to <0.0001). Mean serum/fluid ratios were lowest in ovarian cancer (FSH ¼ 2.91, LH ¼ 4.19).Our findings support the hypothesis that gonadotropins are involved in ovarian carcinogenesis and suggest that gonadotropin serum/tumor fluid ratios could be of value in the differential diagnosis of functional and organic cysts of the ovary.