Endometriosis is an oestrogen-dependent disorder that can result in substantial morbidity, including pelvic pain, multiple operations, and infertility. New findings on the genetics, the possible roles of the environment and the immune system, and intrinsic abnormalities in the endometrium of affected women and secreted products of endometriotic lesions have given insight into the pathogenesis of this disorder and serve as the background for new treatments for disease-associated pain and infertility. Affected women are at higher risk than the general female population of developing ovarian cancer, and they also may be at increased risk of breast and other cancers as well as autoimmune and atopic disorders. Clinicians should assess and follow up affected women for these and other associated disorders. There will probably be a new repertoire of approaches for treatment and perhaps cure of this enigmatic disorder in the near future.