It is well known that certain aspects of endometriosis are similar to those of malignant disease. For example, like cancer, endometriosis can be both locally and distantly metastatic; it attaches to other tissues, invades, and damages them. Endometriosis is a common disease that does not create a cachectic or catabolic state, and is rarely fatal. There are, however, numerous reported cases of malignancy arising from endometriotic deposits and substantial histologic evidence that endometriosis is associated with endometrioid carcinoma and clear cell carcinoma of the ovary. A large review article by Mostoufizadeh and Scully investigated the association between endometriosis and endometrioid carcinoma, noting that women who had both diseases tended to be younger [1]. They found no association between endometriosis and serous or mucinous carcinoma of the ovary, and reported that malignant transformation of endometriosis was rare and associated with the use of exogenous estrogens. An epidemiological study of Swedish women reported a higher incidence of breast and ovarian cancer and non-Hodgkin's lymphoma in women with endometriosis compared with controls [2]. Vercellini and colleagues also reported a higher incidence of endometrioid and clear cell carcinoma in women with endometriosis compared with controls [3]. Mutations in genes associated with galactose metabolism have been identified as one possible mechanism for this association. These mutations are more common in ovarian cancer and have been reported to be more common in women with endometriosis. We compared 78 women with endometriosis with 248 controls and were unable to demonstrate an increased frequency of these mutations in any of these groups.