FOR AN OFFENDER TAXONOMY TO BE USEFUL IT MUST BE COMPLETE, RELIABLE, VALID, DYNAMIC, ECONOMICAL, AND CONTAIN CLEAR OPERATIONAL DEFINITIONS AND IMPLICATIONS FOR TREATMENT. TO DETERMINE WHETHER A TAXONOMIC SYSTEM BASED ON A PAPER-AND-PENCIL TEST OF PERSONALITY, THE MINNESOTA MULTIPHASIC PERSONALITY INVENTORY (MMPI), COULD MEET THESE CRITERIA A SERIES OF STUDIES WERE UNDERTAKEN OVER A 5-6 YEAR PERIOD. ORIGINAL TESTING INVOLVED A SAMPLE OF OVER 2,500 YOUTHFUL OFFENDERS, 18 TO 27 YEARS OLD, AT THE TALLAHASSEE (FL) FEDERAL CORRECTIONAL INSTITUTION. FROM MMPI PROFILES OF THESE INMATES CLASSIFICATORY RULES WERE DEVISED FOR NINE PROFILE CLUSTERS. FURTHER REVISION AND REFINEMENT OF THESE RULES RESULTED IN A SET OF 10 RULES. A COMPUTER PROGRAM EMBODYING THESE RULES WAS DEVISED. FINAL REVISION OF THE RULES RESULTED IN 96 PERCENT OF A SAMPLE OF PROFILES BEING CORRECTLY ASSIGNED TO ONE OF THE 10 TYPES BY A CLINICIAN AND/OR A COMPUTER. THE OPERATIONAL DEFINITIONS FOR THESE 10 TYPE GROUPS ARE PRESENTED TOGETHER WITH THE DEFINING PROFILE CHARACTERISTICS, THE MEAN GROUP PROFILE, AND THE PROPORTION OF THE TOTAL SAMPLE PER GROUP. A FURTHER STUDY OF THE DEFINING CHARACTERISTICS OF OFFENDERS IN EACH GROUP WAS UNDERTAKEN WHICH CONTRASTED A VAST ARRAY OF PERSONALITY, ATTITUDE ABILITY, ACHIEVEMENT, DEMOGRAPHIC, AND CRIMINAL AND FAMILY HISTORY DATA. RESULTS INDICATED SIGNIFICANT DIFFERENCES AMONG THE GROUPS IN TERMS OF BEHAVIOR, SOCIAL HISTORY, LIFE STYLE, AND PERSONALITY PATTERNS. THESE MODAL DEFINING CHARACTERISTICS ARE PRESENTED FOR EACH OF THE GROUPS TOGETHER WITH IMPLICATIONS FOR TREATMENT SETTING AND METHODOLGY. ONGOING RESEARCH TO DETERMINE ADDITIONAL INTER/INTRAINDIVIDUAL AND INTER/INTRAGROUP DIFFERENCES ARE BEING UNDERTAKEN. GENERAL APPLICATION OF THE 10 TYPES TO OTHER SAMPLES IS ALSO BEING INVESTIGATED. PROJECTED RESEARCH PLANS ARE OUTLINED AND RECOMMENDATIONS FOR ADDITIONAL FUTURE RESEARCH ARE MADE. FOR SELECTED READINGS, SEE NCJ 47696-47700. (JAP)