Objectives: The aim of this work was to compare concentrations of adiponectin in the serum of obese women with endometrial cancer, endometrial hyperplasia with atypia, and normal endometrium. Methods: We enrolled 105 obese women treated at the Department of Gynecological Surgery and Oncology of Adults and Adolescents. The patients were allocated to groups depending on the histological diagnosis (R - endometrial cancer, P - polyps, K - normal endometrium). We subdivided group R depending on the stage and grade of cancer. Results: Significantly lower concentrations of adiponectin were found in patients with endometrial cancer (mean 15.28 μg/mL) as compared with polyps (29.94 μg/ml, p < 0.001) or normal endometrium (22.7 μg/mL, p < 0.05). Stage of cancer had no significant effect on the adiponectin level. When cancer grade was compared, lower levels of adiponectin were observed in patients with G3 (12.86 μg/ml) than G1 (19.04 μg/mL, p < 0.05). Conclusion: Reduced levels of adiponectin may represent an independent risk factor for endometrial cancer