THYROID tissue develops fairly frequently in ovarian dermoids (table 1), although it is usually no more than a microscopic portion of the tumor. There is, however, a rare type of ovarian tumor, known as struma ovarii, in which thyroid tissue is a major constituent.1 Some of these ovarian goiters are obvious teratomas, containing besides thyroid such tissues as skin, teeth, brain and intestinal epithelium. Others consist entirely of thyroid or of thyroid in association with a cystoma. Boettlin in 1889 was the first to note the presence of thyroid tissue in an ovarian dermoid. Wilms, Merttens and Kroemer published reports of similar cases. Then Gottschalk in 1899 described an ovarian tumor composed entirely of thyroid-like tissue. Thyroid tissue in the midst of a dermoid was not remarkable, but an ovarian tumor composed entirely of thyroid seemed improbable. Gottschalk concluded, despite its structural similarity to thyroid, that the tumor was