An uncommon case of concurrent tumors: Unilateral Wilm's tumor with contralateral retroperitoneal teratoma in a 3-year-old child.

Wilms tumor is the most common renal malignancy in children, while retroperitoneal teratomas are rare. Their simultaneous occurrence at distinct sites is exceptionally rare. We report a 3-year-old child with right-sided Wilms tumor and a contralateral retroperitoneal mass. Imaging and biopsy raised concern for metastasis versus second primary tumor. Preoperative chemotherapy led to regression of the renal lesion but stability of the retroperitoneal mass. Surgical resection confirmed residual right side high-risk Wilms tumor and contralateral mature cystic teratoma. This case highlights diagnostic challenges and emphasizes the importance of early recognition, multidisciplinary planning, and tailored therapy in achieving successful outcomes.