Immature teratomas of the ovary represent less than 1% of all ovarian teratomas. They contain several tissues that derive from the three embryological layers: ectoderm, mesoderm and endoderm. They are rarely associated with peritoneal implants that are essentially composed of mature glial tissue, and of benign evolution. We report the case of a 37-year- old woman who presented an immature teratoma of the right ovary that recurred seven years later as a malignant neuroepithelial peritoneal tumor resembling a glioblastoma. Glioblastoma was diagnosed at a second recurrence six months later. We discuss the histopathogenesis of peritoneal implants secondary to immature teratomas.