INTRODUCTION: Fetus in fetu is a rare abnormality secondary to the abnormal embryogenesis in a diamniotic, monochorionic pregnancy. It is a rare pathological condition and fewer than 100 cases have been reported in the literature.

CASE PRESENTATION: A 2 month old girl with an abdominal mass since birth, was referred to the Cancer Institute with a suspected diagnosis of a Wilms' tumor. Conventional radiograph of the abdomen revealed a mass containing numerous calcifications. CT scan showed a heterogeneous retroperitoneal mass containing well-defined calcified structures. The decision was made to recommend surgical exploration and the mass was successfully excised. Physical examination of the mass with review of literature confirmed the diagnosis of fetus in fetu.

CONCLUSION: Although it is a rare condition imaging may play an important role in the correct prospective diagnosis of fetus in fetu. Surgical excision is the recommended treatment.