The beneficial effects of external irradiation for the superior vena cava syndrome secondary to malignant disease have been studied by numerous observers. One aspect that has received little emphasis is the nature and extent of the pathologic findings at necropsy. The purpose of this report is to focus attention on these findings and to consider the apparent effects of external irradiation on mediastinal pathology and patient survival. Methods And Materials Eleven hundred and fifty cases of primary lung cancer were treated in the Veterans Administration Hospital, Philadelphia, between January 1953 and November 1967. In 941 patients the diagnosis was confirmed by histologic examination. Sixty-nine patients with superior vena cava syndrome were treated in the radio-therapy department, and in 57 of these there was histologic proof of bronchogenic carcinoma. Three had biopsy-proved lymphoma (Table I). In 15 per cent of the patients with primary lung cancer seen in the Radiotherapy Department and in 5.7 per cent of all hospital cases of primary lung cancer, the superior vena cava syndrome was either a presenting complaint or a development. Radiotherapy at this hospital has been administered with a 250 kV unit with a Thoraeus II filter, resulting in a beam with a half value layer of 3 mm Cu. Our experience over a fifteen-year period reflects the application of changing concepts in the treatment of superior vena cava syndrome. Several patients were treated in 1953 with the grid technic. During the middle and later 1950's most patients were given small initial doses with increasing daily increments to a total dose which averaged 2,900 rads. Pretreatment with one or two doses of nitrogen mustard or concomitant steroid administration was used in some patients, presumably to reduce so-called radiation edema. Approximately two-thirds of the patients were given diuretics, usually mercurials, during the course of x-ray therapy. An occasional patient was digitalized. These various adjunctive measures have not been evaluated. After Jan. 1, 1961, our treatment protocol became rather standardized. All patients received a tumor dose of 200 rads per day, 1,000 rads per week, to a total of 4,000 rads. Consequently, the total dose since 1961 exceeds the earlier dose by an average of 1,100 rads. The survival and the clinical response were significantly improved (TABLE II). Results And Discussion Response to radiation therapy can be judged by clinical evaluation, measurement of venous pressure, venography, duration of survival, and autopsy findings. Clinical response to therapy, i.e., clearing of venous obstructive signs and symptoms, was graded as either (a) marked or complete or (b) poor or unimpressive.