Contex: currently in clinical practice using the WHO classification 2014, involving the separation of endometrial hyperplasia (EH) into two groups: EH without atypia and atypical EH. However, this classification also suggests the use of the term endometrial intraepithelial neoplasia (EIN) as a synonym of atypical EH, while diagnostic categories have different criteria. In particular, the diagnosis of EIN does not necessarily presuppose the presence of atypia of epithelial cells, but only suggests that the epithelium of the affected glands should be different from the surrounding epithelium. From our point of view when using the WHO classification 2014 and all of the EIN criteria except atypia is necessary to exclude clonality lesion by research of the expression of PTEN in order to avoid underestimation of the severity of the disease. The objective of the research was to identify whether the application of different systems lead to the formulation of different diagnoses, implying different treatment approaches. Methods: For analysis we used histological and immunohistochemical (IHC) (determining PTEN expression) methods and classification system of the WHO 2003, WHO 2014 and EIN. Patients: a pilot study included 22 women with a histological diagnosis of EH without atypia (WHO 2014). Interventions: Performed curettage of the endometrium for histological and IHC study and valuation of medication by three independent pathologists. Results: In the histological examination complex EH without atypia (according to the WHO classification 2003), EH without atypia (according to the WHO classification 2014) were diagnosed. In the valuation of medication on the system of EIN with IHC study of PTEN in four cases (18%) EIN was diagnosed on the basis of all classification criteria and a complete lack of expression of PTEN in the affected area. Conclusion: the Diagnostic criteria for EIN to EH samples without atypia allows to identify the more severe lesions of the endometrium associated with a high risk of endometrial cancer. This approach seems to be promising for allocation of patients groups requiring prolonged hormone therapy and the monitoring of the status of the endometrium.