Abstract
A case of endodermal sinus tumor of the ovary associated with hirsutism and increased testosterone production is described. Electron-microscopic examination revealed accumulation of basement membrane-like material and other ultastructural features consistent with endodermal sinus tumor. Groups of polyhedral cells asssociated with the tumor were found to contain abundant lipid material. These luteinized stromal cells were evidently responsible for the endocrine manifestations.