BACKGROUND Endodermal sinus tumor is a malignant germ cell tumor that generally involves the gonads. Extra-gonadal localization out of midline organs is rare. We report a case of endodermal sinus tumor in the thoracoabdominal wall. METHODS We discuss the case of an infant presenting an abdominal mass detected after a fall from his own height. Studies revealed anemia with abundant intraabdominal fluid and elevated alpha-fetoprotein. During surgery, a left thoracoabdominal wall-dependent tumor was identified, with involvement of the diaphragm and the costal cartilage. Complete resection was performed. Pathology report informed of an endodermal sinus tumor. CONCLUSIONS Abdominal wall location of endodermal sinus tumor is rare. Pathophysiology has not been completely outlined, however, it is presumed to be a consequence of aberrant migration patterns of the primordial cells. Pre-surgical diagnosis remains a challenge due to the low incidence.