Psychogenic or organic? Which is the determining factor, at least in the beginning, of what is commonly called the postconcussion neurosis? When these patients come to the neurologist the symptoms usually are chiefly, or exclusively, subjective. It is difficult to say whether the symptoms complained of are purely of emotional, and therefore psychogenic, origin. The trend of the neurologist's thought in this connection is apt to depend on whether he has learned to stress the psychologic factors or whether, on the other hand, he seeks the structural, organic causes. Our work shows that the structural factors in postconcussion neurosis have not received adequate attention. We were impelled to make this study by two facts. Early in our observation of cases of concussion, we became impressed with the difference in the nature of the reactions from cases of posttraumatic psychoneuroses in which it seemed fair to assume that the injury of