Malignant triton tumor is a subtype of malignant peripheral nerve sheath tumor which presents a rabdomyoblastic differentiation. We report the case of a 14-year-old male with a radical surgical resection of a mediastinal malignant triton tumor of the sympathetic nerve, a rare location for this tumor. Thereafter, he received adjuvant radiotherapy and was reoperated three months later for an early local recurrence. The prognosis for this group of tumors is poor. Radical surgical excision of the tumor followed by radiation therapy must be the treatment of choice.