The studies of the incidence of endometriosis are historically given; the epidemiology and classification of this disease and its clinical manifestations are considered. Particular emphasis is placed on the need of using endometriosis treatment options that assist in reducing the number of radical surgical interventions and in preserving the reproductive function of patients. Treatment should be stepwise, safe, long-term, and individually chosen. There requirements are met with dienogest, a specially designed agent to treat endometriosis, which combines the properties of both 19-nortestosterone (a potent progestogenic effect on the endometrium, a relatively short half-life, and a high oral bioavailability) and progesterone derivatives (an antiandrogenic effect, good tolerability, and mainly local exposure). When given in a small dose (2 mg), the drug is effective in reducing endometrioid lesions and in relieving pain associated with endometriosis, including dysmenorrhea, premenstrual pain, dyspareunia, and diffuse pelvic pain; and, when used long, it is as effective as gonadotropin-releasing hormone agonists. The authors declare no conflicts of interest.