Endometriosis, defined by the development of endometrial tissue outside the uterus, is a benign disease responsible for infertility and pelvic pain. The diagnosis based on a detailed gynecological history and a careful clinical examination should be done as early as possible in order to treat patients correctly. Medical treatment is not appropriate in all cases and surgical treatment should be proposed but morbidity is related to the severity of the lesion. Ectopic implantation of endometrial cells needs complex interactions between host tissue and epithelial endometrial cells. The conditions for the development of endometriosis are estrogeno-dependent growth of endometrial cells, induction of angiogenesis and lymphangiogenesis. Principal cellular and molecular factors of angiogenesis, lymphangiogenesis and fibrosis should be identified in order to develop new therapeutic strategies of endometriosis.