Aim: To assess the expression of mismatch repair (MMR) proteins MSH2 and MLH1 and carry out microsatellite analysis in patients with endometrial cancer (EC) with regard to the family history of cancer. Materials and Methods: Morphological and immunohistochemical study was performed on tumor tissue samples of 49 EC patients. Microsatellite instability was determined using PCR with primers which flank microsatellite region BAT-26. Results: A tendency to a decreased expression of both MSH2 and MLH1 markers in a group of EC patients with a family history of cancer as compared with a group without aggregation of cancer in family history was observed (labeling index — LI — was 36.1 ± 8.1% and LI 20.7 ± 9.1% versus LI 48.0 ± 5.8% and 33.8 ± 5.8%, respectively). It was determined that the number of EC patients with tumors deficient by expression of MMR markers was reliably higher in a group of patients with a family history of cancer than in a group of patients without aggregation of cancer in fami ly history (р < 0.05). It was shown that in a group of EC patients with a family history of cancer, MMR-proficient tumors were detected in 38.5% of cases. Microsatellite instability was determined in 10.7% of EC patients including one patient with aggregation of Lynch-associated tumors in family history. Conclusion: Family history of cancer of EC patients is associated with malfunctioning of the MMR system as well as may be related to alternative molecular mechanisms.