Endometriosis is a disease characterized by a benign growth of tissue identical to the endometrium outside the uterine cavity with an accompanying inflammatory process. The exact prevalence of external genital endometriosis (EGE) is unknown. According to some data, the prevalence varies from 2% to 10% among the general female population and up to 50% among women with established infertility. Currently, there is no single theory that could fully explain the causes and mechanisms of the development of the disease. The etiopathogenesis of endometriosis is widely discussed and remains uncertain. The main clinical markers of the disease are chronic pelvic pain, dysmenorrhea, dyspareunia, and infertility. The progressive and recurrent course of EGE with a significant deterioration in the quality of life of women is the main motivation for the scientific community in the search for radical therapeutic methods. The main goal of therapy is to reduce pain, correct reproductive dysfunction, prevent / slow down the occurrence of such long-term consequences associated with endometriosis, such as fibrosis, adhesions and malignant transformation. Available advanced technologies aimed at establishing and studying the pathophysiology of endometriosis have made it possible to optimize therapeutic strategies. However, many controversial issues still arise in routine clinical practice. This article will provide an overview of the general basic concept of disease pathogenesis and highlight the role of hormonal treatment (dienogest) in women with endometriosis.