We describe a rare case of an extragonadal retroperitoneal pure yolk sac (endodermal sinus) tumor in the paraaortic region. Radiologic investigation, which included abdominal ultrasound ,computed tomography (CT), and magnetic resonance imaging (MRI) showed a large soft tissue mass occupying the inter paraaortic, renal, pancreatic and splenic region. Radionuclide bone scans demonstrated no bone metastases. The serum alpha fetoprotein (α-FP) level was high; however β-HCG was normal. Pathologic examination of the surgical specimen showed extragonadal yolk sac tumor. After postoperative chemotherapy, follow-up CT revealed decreased residual tumoral tissues and α-FP level returned to normal.