On the basis of visits to mental hospitals in 17 countries on 5 continents, supplemented by some study of the literature, the following conclusions seem warranted.1. There are now sufficient data available to make preliminary basic generalizations concerning the etiology, incidence, symptomatology, diagnosis, and treatment of mental illnesses in various parts of the world.2. The major psychoses take the same form in many regions, regardless of race, physical environment, cultural background, and socio-economic situation: in the sense that a well-trained clinician entering a mental hospital in any one of a number of different countries scattered on all the continents can diagnose by inspection (say) 25% of the patients; can diagnose after a few moments of listening even to a language he does not understand (say) another 25%; and will have similar difficulties almost anywhere in diagnosing the remainder. This means that well-developed catatonia, hebephrenia, mania, and melancholia are common afflictions in widely scattered countries.3. In borderline cases and neuroses, a well-trained clinician with a command of the language can sometimes penetrate the veneer of even the most exotic culture in a very short time, say a quarter of an hour, sufficiently to proceed thenceforward as usual in constructing a working diagnosis and a preliminary treatment program.4. In tropical countries, there tends to be an increased incidence of toxic confusional psychoses among hospitalized patients, so that they may even outnumber the usually predominating schizophrenias. These cases often respond to nutritional and general hygienic measures.5. Neither the proportionate size of the mental hospital population, the admission rate, nor the total psychiatric patient load, including dispensaries, can be considered a reliable index of the incidence of mental illness in a given region of the world. These factors seem rather to depend on the quality and quantity of the facilities available and on the local attitude toward psychiatric treatment. The tendency in all areas studied is to fill good hospitals and clinics as rapidly as they are provided and public opinion permits.6. According to the psychoanalytic literature from various parts of the world (e.g., The International Journal of Psycho-Analysis with editors from 17 countries), the neuroses seen in private psychoanalytic practice are always associated with a history of disturbances in infantile psychosexual development, regardless of racial, physical, cultural, and socio-economic background. The majority of all psychiatrists, however, do not accept this universality.7. Concerning symptomatology, this may be differentially influenced in many cases by racial, physical, cultural, and socio-economic factors, both in the relative predominance of different mental mechanisms and in the psychotic contents. It is possible that the incidence of various neuroses is also influenced by these factors: e.g., deaf-mutism in Russian soldiers(37) versus anxiety states in American soldiers.8. In regard to therapy, the following instruments seem to be universally effective in a percentage of appropriate cases: electroshock, electronarcosis, insulin therapy, continuous sedation, surgical interruption of nervous pathways, Rawulfia derivatives, and other drugs; psychoanalysis, psychotherapy, and group psychotherapy.9. The following qualities in the therapist seem to be universally therapeutic, regardless of the racial, cultural, and socio-economic backgrounds of the parties concerned, as far as the international literature and personal experience demonstrate: loyalty, sincerity, respectfulness, and availability. These may all be subsumed under the single rubric of trustworthiness (rather than the popular label of "love," which is either not necessary or "not enough"). As someone lightly remarked, a really good Boy Scout will have therapeutic successes anywhere. Witch-doctors appear to have a different approach, but they seem to be most effective locally.10. In view of all this, the following tentative formulations may be made concerning the growing science of comparative psychiatry. Its first problem is to confirm (or refute) the impression that the basic psychogenesis, epidemiology, symptomatology, diagnosis, and response to treatment of mental illnesses are the same throughout mankind. Its second problem is to study the more superficial differences in epidemiology, symptomatology, and therapeutic response which may be influenced by physical environment, racial and cultural background, and socioeconomic situation. The first problem lies primarily within the sphere of the clinician and can best be assessed by him alone. The second requires the assistance of qualified geographers, anthropologists, and sociologists, with the ancillary services of medical epidemiologists and psychologists.