Rotation therapy is a technic of irradiating deep-seated lesions by rotating the patient in the beam or by moving the tube about the patient. Within certain limitations this method offers a more symmetrical distribution of radiation and a more advantageous ratio of depth to skin dosage than cross-firing with stationary fields. Although the idea was first suggested in 1906 by Kohl, it was not until 1937 that it was tried. Since 1937 numerous workers, notably Du Mesnil de Rochemont, Dessauer, Jensen, Nielsen and Nakaidzumi, have studied the basic relationships by calculation, measurements on phantoms, and clinical trials on patients. The object of the procedure is always to have the lesion in the beam while every other part of the body is irradiated only as it passes through the beam on the tube side of the lesion and on the opposite side (Fig. 1). This is easily accomplished by rotating the patient in the erect posture on a simple turntable with the beam horizontal and perpendicular to the axis of rotation. The patient may sit on a stool or stand up, depending upon the part of the body being treated (Fig. 2). Support is rarely necessary. Moving the tube about the patient presents formidable and expensive mechanical problems. The turntable (Fig. 3) need not be elaborate or expensive. A disk of wood or metal, supported around the edge on roller bearings, and driven by a worm gear and a quarter horsepower motor, is all that is needed. It should be at least 3 feet in diameter and of strong enough construction to accommodate heavy patients. The rate of rotation is immaterial so far as dosage distribution is concerned. European workers have made elaborate set-ups so that the position, particularly in the treatment of carcinoma of the esophagus, may be continuously controlled by fluoroscopy. They have used very small fields. While such an arrangement may be desirable, it is not, in my opinion, necessary. The small fields offer certain disadvantages, since peripheral parts of a lesion, particularly an infiltrating carcinoma, cannot be located accurately. The field, therefore, should be wider than the known lesion. If the patient is turned very slowly, a small change in position will produce a serious disturbance in distribution. If, however, the patient is turned fifteen to twenty-five times during a treatment, a small change in position during one revolution, or part of one, will have little effect. One complete turn a minute is a satisfactory rate. It is slow enough so that the patient does not get dizzy and allows an adequate number of turns per treatment. The distribution of radiation in the body during rotation is different than with stationary fields. To illustrate this, let us assume an ideal situation, where a cylindrical body is irradiated through a portal which is narrow in proportion to the diameter. The distribution may be represented by a bell-shaped curve (Fig. 4).