1. Five hundred cases that were diagnosed "post-traumatic psychoneurosis" were studied statistically with regard to the following variables: a. Variables of historical data, b. Variables of objective signs, c. Variables of symptom complexes, d. Variables of course of the disorder, and e. Variables of results of therapy. 2. Controls consisted of non-traumatically induced psychoneuroses and neurologically injured patients who did not develop psychoneuroses. 3. Definitions are given to clarify a subject that has been confusing to both the medical and the legal professions. 4. Differential diagnostic problems are presented, with a classification of psychogenic factors in other syndromes sometimes found post-traumatically. 5. A series of legal questions compiled from legal examinations and cross-examinations of psychiatrists at hearings and in courts are presented for study. 6. Post-traumatic psychoneurosis is probably the most misunderstood condition that occurs in medico-legal cases, and to make it understood to judges, referees, commissioners and juries, as well as to attorneys and doctors, it must be made tangible, clearly-cut, definite and therefore diagnostically valid. These diagnostic criteria eliminate the arguments of objective versus subjective, for everything in medicine is both objective and subjective.