WITHIN the confines of the mediastinum arise a heterogeneous group of tumors which, by reason of their peculiar derivation, their striking radiographic appearance, and their complex pathology, have long possessed a fascination far exceeding their incidence. Over the past 25 years, coincident with the advancement of thoracic surgery, these curious tumors have ceased to hold a purely academic interest and have assumed a more practical importance. Many reports have appeared stressing the hazards inherent in most mediastinal tumors and the minimal risk attending their excision. Yet, there somehow persists an unreasonable tendency to view them with complacency. In reviewing the records from three large hospitals of all patients with the diagnosis "mediastinal tumor" we repeatedly encountered patients in whom a radiographically demonstrable mediastinal mass had been inadequately investigated and therapeutically ignored. Since more and more of these tumors are being discovered in the asymptomatic stage as a result of x-ray