Endometriosis is the female disease and very frequent. The grade differs widely: mildest stages, which do no harm, are occurring as well as severe manifestations destructing parts of the internal genital tract and creating adhesions. The etiology is still not unanimously clarified; there are probably etiologies more than one pathways. Endometrial particles which are capable of implantation can pass through the Fallopian tubes, lymphatic penetration, metaplastic processes or even immunologic deficiencies of macrophages have been accounted for the onset of endometriosis. The diagnostic procedure starts always with laparoscopic inspection. It is the beginning of a serious treatment. Classification is only possible after direct viewing of the pelvic organs. Staging and grading follows the proposal of the American Fertility Society, which is the standard even in non-English speaking areas of the world. The clinical symptoms of endometriosis are varying broadly. The leading symptom is [secondary] dysmenorrhoea. Treatment is managed by steps: I. Diagnostic endoscopic procedures with classification and removal of endometriotic foci so far possible. II. Pharmacologic therapy uses estrogen-progestogen combinations, progestogens, danatrol, GnRh-analogues, even tamoxifen and other regimens. III. Repetitive laparoscopy tries to completely clear from endometriotic remnants. Laparotomy was frequent in former times but is rarely carried out at present, however still mandatory in certain cases. The aim of treatment ist the cure of endometriosis and the reconstruction of a normal genital situation. Infertility is not a rare consequence particularly in severe cases according to stage IV AFS.