J. Y., a 16-month-old Asian girl, presented with suspected gross hematuria. Physical examination revealed the source of bleeding to be the vagina. No masses were palpable on examination and she was otherwise in good health. Urinalysis and multichannel chemistry (Chem 20) panel were normal. Serum a-fetoprotein (AFP) was 16,500 ng./ml. (normal less than 8.9). Ultrasound of the pelvis revealed a 4.5 3 4.5 cm. anterior vaginal wall mass, which was confirmed on enhanced computerized tomography (CT) of the pelvis (see figure). No evidence of distant spread was identified. Cystoscopy and vaginoscopy demonstrated no bladder abnormalities. However, a large friable tumor was seen along the posterior and right wall of the vagina. Endoscopic as well as incisional biopsies were performed. Pathological evaluation of the biopsy specimen revealed a solid tumor, consisting of atypical epithelial cells that formed tubular patterns suggestive of endodermal sinus structures. Shiller-Duvall-like bodies were identified. Immunoperoxidase staining of the tumor was strongly positive for AFP. Diagnosis was vaginal yolk sac tumor, and the patient was started on cisplatin, bleomycin and etoposide. After 2 cycles of chemotherapy repeat CT of the pelvis revealed a dramatic reduction in tumor volume. Following 2 more cycles repeat vaginoscopy and biopsy of a small residual mass on the posterior vaginal wall demonstrated necrosis and a small area of viable tumor. After an additional 2 cycles were given AFP normalized. Repeat CT showed persistence of a small residual mass along the vaginal wall. Exploratory laparotomy was performed with local excision of the residual mass. Histological review revealed fibrosis only with no evidence of tumor. At 6-year followup there was no evidence of residual disease.