To assess the feasibility of Microsatellite Instability (MSI) analysis in uterine cavity washings for detecting endometrial cancer in Lynch syndrome. This was a proof-of-concept study in Lynch syndrome patients, scheduled for hysterectomy. At the beginning of surgical procedure, uterine cavity washings were performed, and sent for MSI analysis. Pathological examination of the uterus was associated with mismatch repair protein expression and MSI analysis. Nine patients were included in the study. Uterine cavity washings were feasible and interpretable in all cases. Final histological report identified 2 endometrial cancers and 7 benign specimens. There was no atypical hyperplasia. Sensitivity, specificity, positive predictive value, and negative predictive value of MSI analysis in uterine washings reached 100% in all cases. Concordance of MSI presence or absence was absolute between uterine washings and final histology. MSI analysis in uterine cavity washings may be a promising screening tool for Lynch syndrome-associated endometrial cancer diagnosis.