Radiologic study is the most important and valuable mode for detection and diagnosis of mediastinal tumors since a large part of patients are asymptomatic when detected and other studies are of little assistance in detection and diagnosis. It is difficult and often impossible to differentiate these tumors radiologically without histologic findings. for this reason and recent advances in anesthesia and thoracic surgery, aggressiveness for surgical trial for diagnosis and treatment has increased. However, it is sometimes impossible to remove tumors completely or even thoracotomy may be needless. so every diagnositc study including roentgenologic study and biopsy should be tried before thoracotomy. 85 cases of mediastinal tumors diagnosed and treated at Seoul National University Hospital during past 8 years were reviewed in respect to the types of tumors, location age incidence as well as radiographic findings. The Results are 1. The commonest tumor was lymphoma being 24 cases(28 2%). Tuberculous lymphadenitis(12 cases 141.%), teratodermoids(11 cases, 12.9%), neurogenic tumors(10 cases, 11.8%) and thymoma(8 cases) rank next in order of frequent. 2. Tumors of middle compartment were 37 cases(43.5%), anterior, 27 cases(31.8%) and posterior, 21 cases(24.7%). 3. Most common tumors of each compartment were teratodermoid in anterior, lymphoma in middle and neurogenic tumor in posterior. 4. 29 cases of the series were proved as malignant, being 34.1%, of which lymphoma was the commonest.