The increased frequency with which in trathoracic masses have been discoverd in the pediatricage group seems to correspond to the increased utilization a typical location and appearance, the range of of possibilities is so great that the diagnosis is rarely made with any certainity before operation. For evalutaion of clinical and tumor which were diagnosed pathologically at Severance Hospital, Yonsei University College of Medicine since 1971. The results; 1. The mediastinal tumors are predominent : 25 cases of mediastinal tumors and 3 cases of pulmonary tumor. 2. The incidence of tumors according to pathologic type is as follow: The malignant lymphoma is most common(12 cases, 45%), next is neruogenic tumor(7 cases, 25%), and Rhabdomyosarcoma 2 cases, benign teratoma 2cases, thymoma 1 case, bronchogenic cyst of mediastinum 1 case. Pulmonary lesion as follow: 2 cases, thymoma 1case, bronchogenic cyst of mediastinum 1 case. 3. The sex incidence in out series shows male predominence(22:6) Under 6 years of age, neurogenic tumor and malignant mesenchymoma are predominent, between 11 to 15 years of agemalignant lymphoma is predominent and between 6 to 10 years age variable types of tumor are observed. 4. The radiological findings are as follows; a. Malignant lymphoma are located at the anterior and/or mid mediastinum with unilateral or bilateral mediastinal widening. The majority show smooth margin and lobulations on their borders. b. Neurogenic tumors are located in posterior mediastinum. Their margins are sharp of ill-defined. Specimen radiolography found minimal calcification in 1 case. Rib erosion and intercostal widening are noted in 2cases. c. Teratoma are all located in anterior mediastinum with well defined smooth margin. Curvilinear calcification in 1 case. d. Malignant mesenchymoma are manifested as irregular shaggy bordered mass in lungparenchyme. 1 case show multiple granular calcification in the mass.