Endometriosis is characterized by presence of endometrial tissue outside the uterus. Prevalence is estimated at 6-10% in the general female population and many patients experience pain and/or infertility. Diagnosis is achieved by laparoscopic intervention followed by histological confirmation of viable endometriotic tissue. Mild cases are managed medically with contraceptive steroids and non-steroidal anti-inflammatory agents. Surgery provides relief to women in pain but symptoms recur in 75% of cases within 2 years. Starting with menstruation, we have categorized endometriosis into six stages, namely (1) shedding of cells, (2) cell survival, (3) escape from immune surveillance, (4) adhesion to peritoneum, (5) angiogenesis and (6) bleeding. In most of these biological processes, which resemble metastasis, transforming growth factor-beta (TGF-betas) and their high-affinity receptors are involved directly or indirectly. TGF-betas are abundantly and differentially expressed in the endometrium under hormonal control. Although they are preferentially synthesized in the stroma, glands and macrophages also secrete TGF-betas into the uterine fluid, where interaction with preimplantation embryos is suspected. Because mRNA and protein expression of all three TGF-betas is increased around menstruation, we suggest that TGF-betas might be involved in initiation of menstruation. Furthermore, because of high postmenstrual TGF-beta3 levels, we suppose that it might participate in scarless postmenstrual regeneration of endometrium. Our suggestions pave the way to novel routes of investigation into the roles of TGF-betas during menstruation and endometriosis.