A case of peripheral medulloepithelioma, a rapidly growing tumor involving the pelvic cavity of a 12-year-old girl, is presented. The diagnosis was supported by expression of vimentin, nestin, alpha-internexin, neurofilaments, and microtubule-associated protein 5 and by characteristic ultrastructure that included absence of cilia or microvilli. Trisomy of chromosomes 2 and 8 was the only detectable chromosomal abnormality. Combination chemotherapy resulted in complete remission. Because some of these rare tumors are sensitive to chemotherapy, their recognition and separation from other neuroectodermal tumors are advisable for better understanding of their biology and determination of optimal treatment.