There is general agreement that pituitary adenomata are frequently responsive to radiotherapy. Since the publications by Gramegna (1) and Béclère (2) in 1909 numerous articles have appeared concerning the favorable action of roentgen rays on pituitary adenomata of all three types. A review of this literature shows that there is a wide variation in the method of giving roentgen therapy. The more commonly employed technics have involved the use of multiple courses of comparatively small doses given at long intervals. The reports have also shown considerable variation in the incidence of successful results. Our own material includes cases which have been treated with roentgen rays by a large variety of technics, and with wide range of total estimated dose delivered to the pituitary. Because of this variation in methods of treatment, it was felt that an analysis of the results with respect to the therapeutic technic and total dosage might yield data suggesting an optimal procedure. The material available for analysis includes 64 cases of pituitary adenomata. Of these, 38 were chromophobic, 21 eosinophilic, and 5 basophilic. The clinical syndromes of these three types of adenomata have been repeatedly described in numerous publications and will therefore not be discussed here. In all cases the diagnoses were established prior to treatment by groups of competent internists, neurologists, ophthalmologists, and radiologists. There were occasional instances, as also reported by others, where different tumors so closely simulated the syndrome of chromophobic adenoma that they were mistakenly treated as such. Only after failure of roentgen therapy, at surgical intervention or postmortem examination, was the true character of the process established. Thus, we had one case of intrasellar meningioma, one case of paraphysial cyst of the third ventricle, and two cases of Rathke pouch cysts without calcification. These 4 patients have been excluded from the series. Such cases of mistaken diagnosis occur in only a very small percentage of the patients with a clinical diagnosis of pituitary adenomata. The proportion is so small that the errors do not significantly alter the improvement rates following radiotherapy. Confirmation of the diagnosis of pituitary adenomata was obtained in 16 of our cases either by surgery or at postmortem examination. Radiotherapy was the primary method of treatment in 61 of the 64 cases. In 13 of these 61 patients, surgery was later performed. Three cases were first treated surgically and were given radiation therapy for postoperative recurrence. The technics employed in treating this series of cases varied mainly in the total dosage delivered, the number of courses given, the treatment period for each series (in days) and the over-all time for the multiple courses (months to years). The physical factors of irradiation were comparatively uniform. They were: 180 to 200 kv.; 0.5 mm. Cu and 1 mm. Al to Thoraeus filtration; h.v.1. 0.9 to 2.0 mm. Cu; target-skin distance 50 to 60 cm. Usually three pituitary fields were employed: frontal and right and left temporal. The field sizes varied from a circle 5.0 cm. in diameter to a rectangle 6 × 8 cm. Occasionally parafrontal, superior, and mastoid fields were employed.