Yolk sac tumor (YST) is seen in two settings: 1) Pure yolk sac tumor is seen in infants and children (usually under 2 years of age). It accounts for more than 80% of testicular germ cell tumors in children and is associated with excellent prognosis. 2) As a component of mixed germ cell tumors in adults, where the prognosis is more guarded. YST displays an amazing variety of architectural patterns. The most commonly seen patterns are microcystic, glandular-alveolar, and papillary. Microcystic pattern is shown in this image. Interconnecting cords and ribbons of tumor cells are surrounded by abundant myxoid stroma.