Summary Objectives: Malignant tumors of the ovary and uterus remain to be a diagnostic and therapeutic problem in Poland, mainly due to the lack of effective diagnosis of their early stages. There is a relation between an impaired immune system, especially the process of inflammation and the pathogenesis of these tumors. The aim of the study was to assess the concentration of calprotectin – a inflammation marker in the serum of women with ovarian or uterine cancer. Material and methods: The study group included 96 women, aged 21 to 72 (mean age: 46.7+/-13.6 years) with the diagnosed and histologically confirmed ovarian or uterine tumor. The control group consisted of 30 women aged 24–60 (mean age 45.6+/-8.9 years), showing no pathological disorders or any inflammations of the reproductive system. The concentration of calprotectin was evaluated with the use of the immunoenzymatic method ELISA using the Calprotectin ELISA (serum) kit by DRG Instruments (Germany). Results: In serum of women with tumors the calprotectin level was significantly higher comparing to the control group (p <0.0001). The highest calprotectin levels in women with ovarian cancer (mean+/-SD: 231.84+/-13.74ng/ml) and uterine cancer (mean+/-SD: 166.23+/-13.36ng/ml) were observed and were significantly higher comparing to women with ovarian serous adenomas (mean+/-SD: 72.60+/-9.75ng/ml) and fibroids of the uterus (mean+/-SD: 72.31+/-9.19ng/ml) (p<0.0001). Conclusions: In women with ovarian and uterine cancer a significant increase in the concentration of calprotectin was observed, suggesting an inflammatory process that accompanies cancer. These changes are especially pronounced in women with cancer, which probably indicates autocrine production of the protein by cancer cells. Estimation of the parameter examined in the serum may improve differential diagnosis of malignant and benign ovarian and uterine cancers, however it requires further investigation.