Mature teratoma arising from an intra-abdominal undescended testis presenting as a fetal abdominal mass.

Teratoma of the intra-abdominal testis is a rare finding in infants. We describe the case of a full-term newborn treated for a calcified abdominal mass which was observed unexpectedly on prenatal sonography. An undescended right testis was also noted. During laparotomy, a twisted retroperitoneal tumor was found just above the right deep inguinal ring. Histological analysis revealed a mature teratoma of the intra-abdominal right testis. The tumor was removed and there was no recurrence at follow-up 1 year later. A teratoma should be considered in cases of fetal abdominal mass, especially when the testes cannot be detected in the scrotum by the 8th month. Prenatal sonographic diagnosis might be possible.