Radiologic study is the most important and valuable mode for detection and diagnosis of mediastinal tumorssince a large part of patients are asymptomatic when first detected and other studies are of little assistance indetection and diagnosis. It is difficult and often impossible to differentiate these tumors radiologically withouthistologic findings. For this reason and recent advances in anesthesia and thoracic surgery, aggressiveness forsurgical trial for diagnosis and treatment has increased. However, it is sometimes impossible to remove tumorscompletely or even thoracotomy may be needless. So every diagnostic study including roentgenologic study andbiopsy should be tried before thoracotomy. 85 cases of mediastinal tumors diagnosed and treated at Seoul NationalUniversity Hospital during past 8 years were reviewed in respect to the types of tumors, location and ageincidence as well as radiographic findings. The results are 1. The commonest tumor was lymphoma being 24 cases(28.2%). Tuberculous lymphadenitis(12 cases, 14.1%), teratodermoids(11 cases, 12.9%), neurogenic tumors(10cases,11.8%) and thymoma(8 cases) rank next in order of frequency. 2. tumors of middle compartment were 37cases(43.5%), anterior, 27 cases(31.8%) and posterior, 21 cases(24.7%) 3. Most common tumors of each compartmentwere teratodermoid in anterior, lymphoma in middle and neurogenic tumor in posterior. 4. 29 cases of the serieswere proved as malignant, being 34.1%, of which lymphoma was the commonest.