An immature teratoma with predominant malignant retinal anlage component occurred in the ovary of a 17-year-old woman. Karyotype analysis from Qbanded preparations revealed that the tumor was parthenogenically derived and exhibited chromosome instability and aneuploidy. On light-microscopical examination, the malignant elements resembled retinal anlage. Ultrastructurally, large, polygonal, pigmented cells had features of ependymal epithelium: a continuous, welldeveloped basal lamina; microvilli; parallel arrays of rough endoplasmic reticulum; and very large, densely pigmented melanosomes. Adjacent cells identified by light microscopy as immature neuroglia contained glial fibrillary acidic protein by immunohistochemical staining. The presence of neuroglia, not a feature of tumors of neural crest origin, and the ependymal characteristics of the pigmented cells indicate that the neoplasm was most likely of neural groove derivation.