In June 1939, one of us (R. G. S.) in collaboration with Bradford1suggested a group of criteria that could be relied on in the clinical diagnosis of a herniated nucleus pulposus at the fourth or fifth lumbar interspace. These criteria were based on a series of 10 cases in which surgical procedures were done without the aid of contrast myelography. Now, after a larger experience, we are reporting on the success of these criteria and amplifying those points which have been shown to be of the greatest importance in diagnosis. We have avoided the term "protruded intervertebral disk" because we do not consider that it accurately designates the pathologic process in many cases. In order for the disk to produce symptoms we believe the annulus fibrosus must have been ruptured or torn, and if the nucleus pulposus is extruded through the tear a certain group of symptoms will