FOR the past ten years, this Clinic has been interested in roentgen pelvimetry. During that period, we have, by means of numerous communications (see references), endeavored to emphasize the importance of applying roentgenometric methods of diagnosis to the problems of pelvimetry (6), fetal cephalometry (8, 9, 10), and the determination of fetal maturity in utero. At the present time we are convinced that only by roentgenometric means may the true proportions of the superior strait be determined, and, furthermore, that the ordinary external methods of pelvimetry are not only occasionally fallacious, but they may be quite misleading. The present communication deals primarily with the method that we are now employing for pelvimetry. For those interested in fetal cephalometry, attention is directed to references to that subject (8, 9, and 10). In this communication it is the intention to repeat somewhat the description of the technic described in 1929 (6) and, in addition, to demonstrate a modification which may prove useful. Any procedure of this kind, to be of use, must be simple, rapid, and accurate. Furthermore, it must be available for use by others than experts in roentgenologic or obstetric diagnosis. All of these conditions seem to be fulfilled by the method herein described. Indeed, for the past two years the majority of our pelvigrams have been taken solely by a technician trained in our Roentgenologic Department. Centimeter Grid Method Our procedure in this method may be summarized by stating the following: 1. The patient is placed on the roentgenographic table in the semirecumbent position. 2. The level of the superior strait above the sensitized film is established (Fig. 1). 3. The tube target is centered about 5 cm. posterior to the symphysis, at 32 in. from the sensitized film. The exposure is made. 4. The patient is removed from the table, the tube target and sensitized film remaining in situ. 5. A lead plate, or centimeter grid, with perforations exactly 1 cm. apart, is introduced into the same plane as that previously occupied by the superior strait and a second (flash) exposure is made on the same sensitized film as was used in the previous exposure (Fig. 3). 6. Development of the film shows the outline of the superior strait and the shadows of the perforations, the distance between which represent centimeters in the plane of the superior strait (Fig. 4). The anteroposterior and transverse diameters of the superior strait may be read directly. In addition, a pelvigraph of the superior strait in its true proportions may be drawn on centimeter-squared paper by following the course of the shadow of the superior strait and transcribing it (Fig. 6). In the modification presented later in this communication this becomes a matter of simple tracing. Points in Detail