1. Forty per cent of the yearly admissions to the Psychopathic Department are committed to some one of the state hospitals.2. In 1203 cases we have ascertained the diagnosis made by the other institution, together with notes concerning the condition of the patient.3. An average of 6 per cent of cases receive no diagnosis at the Psychopathic. Excluding these, the diagnoses of other institutions agree with ours in 83 per cent of cases.4. Of the transferred cases, 41.6 per cent received a diagnosis of dementia precox—the other institutions agreeing in 89 per cent; 13.3 per cent were diagnosed manic depressive, with agreement of 82 per cent; and 13 per cent were cases of all forms of neurosyphilis, with agreement in 98 per cent.5. In 8 per cent of the cases the other institution disagreed on first or second report, but eventually made a diagnosis agreeing with ours.6. Accordingly "general impressions" of our diagnostic errors are not borne out by these figures.7. Thirty-nine per cent of the transfers were to the Hospital Department of the Boston State Hospital.8. Excluding 31 unclassified cases, the hospital staff agreed with us in 84 per cent of cases, although in 50 cases they did not at first do so.9. The common causes of errors in diagnosis are: (1) insufficient data, either of history or observation; (2) too great stress on one or two symptoms, particularly certain spinal fluid findings; (3) insufficient stressing of important symptoms; (4) multiplicity of signs; (5) changes in general picture of psychosis; (6) failures of interpretation.10. The necessity for complete analysis from every possible angle is accordingly emphasized, as well as the necessity for careful and orderly interpretation of the data when procured.11. Extensive and intensive consideration of the individual case is the great desideratum.12. Since, with a good working technique, diagnoses can be so easily determined in all except the unusual cases, we can pay more attention to treatment than is now usually the case; at the same time bringing to bear on each case all modern methods, laboratory or other, which will aid in understanding the processes of disease.