In order to localize accurately a spinal cord tumor—and by "localization" we mean not only the diagnosis of the level of the new growth but also the exact relations of the growth to the cord—a definite classification of the position of such growths with reference to the surfaces of the spinal cord is necessary. We have, for many years, grouped our tumor cases in the following manner (Fig. 1,AandB). All growths on the posterior aspect of the cord, whether in the median line or laterally, behind the posterior nerve roots, are classified as posterior growths; those that lie on the lateral aspect of the cord, in front of the posterior roots but behind the dentate ligament, we call dorsolateral growths; those that lie laterally, in front of the dentate ligament but behind the anterior roots, we call ventrolateral growths; finally, those that lie on the anterior aspect