Extrarenal Wilms' tumor of the ovary is a very rare tumor likely derived from embryonic mesonephros. We present the first reported case of a teratoid extrarenal Wilms' tumor of the ovary with a short review of the existing literature. In the case, a 26-year-old woman presented with back pain and was found to have a dermoid cyst; three years later, she presented again, now pregnant, with severe abdominal pain. She was diagnosed with an immature teratoma consisting of a Wilms' tumor (immature component) arising within a mature teratoma and treated exclusively with surgery and surveillance. The recovery from surgery was uneventful and the patient remains without evidence of disease with eleven months of follow-up.
Keywords: Immature teratoma; Wilms' tumor of ovary.