[Intraperitoneal testicular fetus in fetu].

A 5-month-old boy presented with a right flank abdominal mass. Plain film of the abdomen showed a vertebral column within the mass. Surgery confirmed the diagnosis of fetus in fetu developed within an ectopic intraperitoneal right testicle. Fetus in fetu differs from teratoma by the presence of axial skeleton and organogenesis. When intratumoral axial skeleton is present, plain films are sufficient for the diagnosis.