Testicular cancer is the most common malignancy in young men with seminomas comprising almost half of all germ cell tumours. Benign ganglioneuromas are rare tumours derived from the sympathetic nervous system. They usually occur in aldolescents and young adults and are predominantly located in the mediastinum and retroperitoneum. We report a case of a patient with synchronous metastatic testicular seminoma with retroperitoneal lymph node involvement and a benign retroperitoneal ganglioneuroma (RGN) which caused diagnostic and management challenges. The patient had a complete response following combination chemotherapy for his seminoma and subsequently underwent complete resection of his ganglioneuroma.