Clinical descriptions of endometriosis first appeared in 1696. These were isolated cases of interest but clearly of unknown importance. Its clinical significance was reported at the turn of the twentieth century. In 1899, Russell described in a case report an ovarian cyst that contained uterine glands and interconnective tissue suggestive of an endometrioma.1 Clinical interest continued as cases of cysts and peritoneal implants containing “uterine-type tissue” were described.2 Despite an increasing body of information, the condition remained poorly understood. The subject became the focus of a review in 1908 when Cullen published Adenomyoma of the Uterus, which summarized the understanding of endometriosis of the time.3 This publication raised the level of awareness and brought the issue into the foreground of clinical care. Several hypotheses regarding the etiology of endometriosis were proposed. The most prominent was described in 1921 by Sampson4 and is now known as the classic reflux menstruation theory. This theory is one of the more commonly cited of several for the development of endometriosis.