Ganglioneuroblastoma, nodular (GNBn) is a subtype of neuroblastic tumors. This is a rare malignancy typically affecting young children. Few cases are reported in adolescents and adults. The prognosis is related to the surgical excision radicality. Hereby we present a case of a young male patient age 13 from the Horn of Africa presenting with vague symptoms of fatigue and weight loss. Chest X-ray showed a large radiopaque mass occupying the right thorax. The chest Computed Tomograpy confirmed the presence of an 18-cm large mass originating from the posterior mediastinum and invading most of the right hemi-thorax. Surgical excision and histopathology study of the lesion clarified its rare nature: ganglioneuroblastoma nodular with a particular coexistence of a fibrous benign surface encapsulating a necrotic malignant core. In this case of large GNBn in a young adolescent, the surgical resection alone played a curative treatment role.