AimTo investigate the expression of Wilms' tumor 1 (WT1) protein in endometrial adenocarcinoma (EC) and endometrial intra-epithelial neoplasia (EIN). MethodsWT1 protein expression was determined on immunohistochemistry in 30 EC patients and in 20 EIN patients. WT1 protein expression in proliferative (n = 7), secretory (n = 9) and atrophic endometrium (n = 9) and benign endometrial polyps (n = 28) was used as the control group. Cellular and vascular WT1 staining was scored semiquantitatively. ResultsCellular WT1 staining was 67% and vascular positivity was 73% in the EC group. In the EIN group the cellular staining was 100% and vascular staining was 85%. Although all EIN samples were positive for cellular WT1 staining, median cellular staining score was similar to that of EC (median, 2; range, 1-3; IQR, 1.75 vs 2, 0-3, 0.75, respectively). Increasing EC grade and stage were not associated with cellular or vascular WT1 staining score. ConclusionWT1 is expressed in EIN.