MEDICAL literature contains many articles on the subject of the x-ray treatment of acne vulgaris, but comparatively few of them deal with statistics based on a large amount of material that has been under observation for many months or years. Statistics can be misleading, but when properly compiled they are invaluable for the control of impressions. Our knowledge of results obtained with the roentgen rays in dermatology is based largely on impressions. For an accurate therapeutic appraisal, statistics from many workers are required. After a sufficiently large number of such statistical reports have been published, they can be compiled and analyzed in an attempt to formulate an accurate evaluation. Years ago the senior writer believed that with the x-ray treatment of acne vulgaris, with the technic universally employed in this country, permanent cures amounted to 85 or 90 per cent; also, that not more than 20 per cent were cured in a reasonable length of time with methods other than x-rays. Later, this impression was found to be erroneous, as shown by the following statistics based on treatment in private practice, which were published in 1927:2 In this group 60 per cent of the patients were clinically cured with one course of treatment; that is, in four months or less. However, recurrences amounted to approximately 11 per cent. The total number of permanent cures, with one course of treatment, is, therefore, reduced to about 50 per cent. American dermatologists understand what is meant by conventional or routine x-ray treatment of acne vulgaris. For others we briefly outline such treatment: The dose is 75 roentgens (estimated with the condenser type of Victoreen ionization dosimeter with chamber in air) administered to each side of the face (back and chest when necessary) once weekly. The radiation is unfiltered. The kilovoltage ranges from 80 to 100, depending upon whether thermionic or mechanical rectification is used. The effective wave length is approximately 0.68 Ängstrom unit. The approximate millimeters of half value layers in aluminum is 0.571. The maximum number of treatments is 16. Treatment is discontinued as soon as lesions cease to develop. Not infrequently only six, eight, or ten treatments are necessary. Irritating and stimulating topical remedies are interdicted. Attention is given to the general health, hygiene, diet, etc. Remedies by ingestion are given when necessary or advisable. All patients included in our x-ray statistics (in this article) were treated in this manner. At the beginning of treatment we carry out skin tests for toleration to x-rays, If toleration is low, the dose is reduced to about 37.5 roentgens. Also, during the course of treatment patients are tested each week for “impending erythema.” This consists of noting increase of local vasomotor instability, with change of posture, pressure, heat, irritation, etc. “Impending erythema” calls for cessation of irradiation or reduction of the dose.