Two yolk sac tumors that arose in the mesentery of the jejunum and the mesentery of the transverse colon of two male patients, aged 2 and 17 years, are reported. Both patients had abdominal masses. The tumors measured 9 and 11 cm in maximum dimension. One of them grew into the bowel lumen. Microscopically, both neoplasms exhibited several of the typical patterns of yolk sac tumor and stained immunohistochemically for alpha-fetoprotein. Both patients received chemotherapy postoperatively and are alive, but follow-up is short. The subject of extragonadal yolk sac tumors is reviewed, and histogenetic implications of their occasional origin in the mesentery is discussed.