THE DISCUSSION IS PRECEDED BY A PRESENTATION OF RESEARCH PROBLEMS COMMON TO SUCH STUDIES; E.G., PROBLEMS OF SAMPLING, INCLUDING THE WELL-KNOWN PROBLEMS OF CONTROL GROUPS; PROBLEMS OF COMMENSURABILITY BETWEEN SAMPLE UNITS; AND PROBLEMS REGARDING INCOMPLETENESS OF PSYCHOSES, (E.G., THEIR DARK FIGURE). RESULTS OF THE 11 STUDIES REVEAL THESE FINDINGS: (1) HOMICIDE IS RELATIVELY FREQUENT WITHIN THE TOTAL DELINQUENCY OF SCHIZOPHRENIC CRIMINALS, AND IT PLAYS AN ABSOLUTELY DOMINANT ROLE AMONG THE CRIMES COMMITTED BY WOMEN WHO SUFFER FROM ENDOGENOUS DEPRESSIONS; (2) SEXUAL OFFENSES ACCOUNT FOR ABOUT 50 PERCENT OF THE TOTAL DELINQUENCY OF THE MENTALLY DEFICIENT BUT ALSO PLAY AN IMPORTANT PART IN THE DELINQUENCY OF SCHIZOPHRENICS; (3) PROPERTY OFFENSES REPRESENT THE MAJOR DELINQUENCY COMMITTED BY EPILEPTICS AND ARE QUITE FREQUENT OFFENSES AMONG THE MENTALLY DEFICIENT; AND (4) ARSON IS COMMITTED BY PERSONS WITH EPILEPSY, MENTAL DEFICIENCY, AND SCHIZOPHRENIA, BUT NOT BY THOSE SUFFERING FROM DEPRESSION. THE SEPARATE DESCRIPTIVE EPIDEMIOLOGICAL STUDY SOUGHT TO CLARIFY THE RELATIONSHIP BETWEEN THE CRIMINALITY OF THE MENTALLY ILL AND CORRESPONDENT CRIMINALITY OF THE MENTALLY SANE. ONLY CASES WITH SEVERE MENTAL DISTURBANCE WERE INCLUDED: FUNCTIONAL AND ORGANIC PSYCHOSES, ALL FORMS OF DEMENTIA, SEVERE MENTAL RETARDATION, AND SEVERE ORGANIC BRAIN SYNDROME. THE TIME COVERED WAS JANUARY 1, 1955, THROUGH DECEMBER 31, 1964. A TOTAL OF 533 CASES WERE DETECTED AND EXAMINED. STUDY RESULTS SHOW THAT SCHIZOPHRENIC OFFENDERS ARE MAINLY MIDDLE-AGED MALES WITH A PARTIALLY INTACT SOCIAL ADAPTATION; DEPRESSIVE OFFENDERS ARE ALMOST ALWAYS MARRIED WOMEN WITH SMALL CHILDREN WHO COMMIT SUICIDE AFTER HAVING PASSED THE CULMINATION POINT OF THE DEPRESSIVE EPISODE; AND THE MAJORITY OF THE MENTALLY RETARDED OFFENDERS COME FROM BROKEN HOMES OR AN ANTISOCIAL MILIEU. HOWEVER, THE MOST IMPORTANT CONCLUSION FROM THIS STUDY IS THAT MENTALLY ILL AND MENTALLY RETARDED PERSONS TAKEN TOGETHER COMMIT NEITHER MORE NOR FEWER VIOLENT OFFENSES THAN NORMAL PERSONS. TABLES AND REFERENCES ARE APPENDED.