Foetus-in-Foetu.

Foetus-in-foetu is a rare malformation in which a monozygotic diamniotic parasitic twin is incorporated into the body of its fellow twin and grows inside it. Less than 100 cases have been reported in literature. One day old newborn male was admitted with antenatal diagnosis of abdominal mass. It was cystic/solid in nature with pressure effects on left ureter and urinary bladder, most likely to be a germ cell tumour. Birth history was uneventful. Exploratory laparotomy was performed and the mass was excised. Physical examination confirmed the diagnosis of foetus-in-foetu. Although it is a rare condition, imaging may play an important role in the correct prospective diagnosis of foetus-in-foetu. Surgical excision is the recommended treatment.