A significant portion of the thoracic masses in childhood are seen in the mediasten. For practical identification of tumors that originate from different tissues, the mediasten is divided into two parts as superior and inferior. The inferior part is subdivided into three portions as anterior, middle and posterior. Mediastinal masses may be malignant or non-malignant. The symptoms vary according to the size and location of the mass. Anterior mediastinal masses are important because of the possibility to press the airways and great arteries. On the other hand, posterior mediastinal masses are also important because of the possibility to extend into intramedullary area and press to nerve roots. According to the symptoms and signs that occur depending on the size and pressure of the mass, immediate treatment may be required. While history and physical examination are important for diagnosis, imaging and laboratory tests are also helpful. Histopathological evaluation is often required for definitive diagnosis.