Germ cell tumors (GCTs) are a heterogeneous group of neoplasms that arise from the primordial germ cells of the human embryo, which are normally destined to produce reproductive cells sperm, or ova. GCTs can be present in both gonadal GCTs and extragonadal GCT sites. Pediatric GCTs are relatively rare tumors with an incidence of 2%-3%. Primary mediastinal germ cell tumors GCTs are very rare extragonadal GCTs that arise in the anterior mediastinum. In this report, we present the case of a 16-year-old boy with primary seminoma arising in the anterior mediastinum. The patient presented with the symptoms of cough, fever, and chest tightness. CT finding was in favor of a large expansive process measuring 12.4x6.7x14.2 cm in the anterior mediastinum, accompanied by a conglomeration of hilar lymph nodes in the level of brachiocephalic veins juncture. Fine needle biopsy and core biopsy were performed transthoracically, under the control of MSCT. Based on histology and immunohistochemistry, the diagnosis of mediastinal germ cell tumor with immunophenotype of seminoma was made. The patient was treated with 4 cycles of chemotherapy by BEP protocol without significant side effects and toxicities. The patient remained disease-free for 16 months. The purpose of reporting this case is to confirm that chemotherapy with cisplatin-based regimens has markedly improved the outcome of adults and children with GCTs as well.