[Endoparasite twin (fetus in fetu)].

Fetus in fetu is a very rare abnormality (estimated incidences: 1 in 500,000 deliveries), and is secondary to a pathological diamniotic monochorionic pregnancy. It consists of a malformed parasitic twin that is found within the body of its sibling. Hardly 70 cases have been reported in the literature since its first description about 1800. Its discovery is usually postnatal. We present two boys: two and half years and eleven days old newborn presented a mass in the retroperitoneum in the left upper abdominal quadrant. There were removed by surgery and contained two independent fetuses. Dissection and radiological study of the fetuses showed an axial skeleton and long bones. It corresponds to the generally recognized diagnostic criteria of fetus in fetu. The embryology, operative procedure, hypothesis and pathology of this condition are discussed and the literature briefly reviewed. The difference between teratomas and fetus in fetu is point.