Severe atypical hyperplasia is a report of endometrial pathologic and histologic changes indicating heavy heterogeneous proliferation of endometrial cells. Atypical hyperplasia is a proliferation and crowding of endometrial glands with a complex structure and a significant decrease in interstitial cells. The glandular epithelium is hyperplastic and shows heterogeneous changes. Atypical hyperplasia is categorized according to the extent of epithelial involvement by hyperplastic cells: 1. Mild: Heterogeneous changes involving the lower 1/3 of the epithelium are considered mild. 2. Moderate: the involvement of the lower 1/3 to 2/3 of the epithelium by the atypical changes is considered moderate. 3. Severe: the atypical changes involve the whole epithelium. Severe atypical hyperplasia can turn into carcinoma in situ and should be emphasized. If patients have irregular vaginal bleeding, they should go to regular hospitals for further diagnosis and treatment by specialists, and if necessary, endometrial biopsy should be carried out to exclude abnormalities.