Light micrograph of atypical endometrial hyperplasia on the left and normal endometrium (lining of the uterus) on the right. On the left, there is overcrowding of glands which are arranged back-to-back with little intervening stroma. The nuclei are enlarged and hyperchromatic. On the right, the glands are scattered with ample stroma in between. In addition, they lack cytologic atypia. Endometrial hyperplasia (EH) refers to an abundance of endometrial glands. It is defined as abnormal proliferation of the endometrial glands relative to the stroma, leading to an increase in gland to stroma ratio (>1). It is an important cause of abnormal, non-cyclical uterine bleeding and a precursor to the most common type of gynaecologic cancer - endometrial carcinoma (EC), endometrioid type. The most common risk factors are unopposed estrogen effect from anovulatory cycles and exogenous use in postmenopausal women.