We report an extremely rare case of extrarenal testicular Wilms' tumor in a 3-year-old boy with intrabdominal undescended left testis. The patient was admitted because of pain and vomiting, with evidence of a huge abdominal mass. At surgery a large tumor arising from the intrabdominal testis was found. Histology showed the classical triphasic Wilms' tumor elements: epithelial, mesenchymal and blastemal areas. Extrarenal Wilms' tumors account for only 3% of all Wilms' tumors and just -100 cases have been reported in literature. Testicular origin is anecdotic. We present histomorphological, histogenetic, clinical, diagnostic, prognostic and therapeutic features of this rare tumor.