THE MASSACHUSETTS LEGISLATURE ENACTED A STATUTE IN 1958 THAT LED TO THE ESTABLISHMENT OF A DIAGNOSIS AND TREATMENT CENTER FOR SEXUALLY DANGEROUS PERSONS. THE STATUTE PROVIDES FOR THE INDEFINITE CIVIL COMMITMENT OF PERSONS WHO HAVE BEEN CONVICTED OF ANY ONE OF A NUMBER OF SEXUAL OFFENSES. CIVIL COMMITMENT IS IMPOSED IN LIEU OF OR IN ADDITION TO A CRIMINAL SENTENCE AND ON OFFENDERS WHOSE MISCONDUCT IN SEXUAL MATTERS INDICATES A GENERAL INABILITY TO CONTROL SEXUAL IMPULSES AND WHO ARE LIKELY TO INFLICT INJURY ON THE OBJECT OF THEIR DESIRE. IMPLEMENTATION OF THE STATUTE INVOLVED THE EVALUATION OF OVER 1,000 SEXUAL OFFENDERS AND THE TREATMENT OF APPROXIMATELY 300 OF THESE OFFENDERS. A DANGEROUS PERSON IS DEFINED AS ONE HAVING A HIGH PROBABILITY OF INFLICTING SERIOUS BODILY INJURY ON ANOTHER. COURTS MAINTAIN THAT PAST MISCONDUCT ALONE IS NOT A SUFFICIENT BASIS FOR THE LABELING AN OFFENDER DANGEROUS AND DOES NOT JUSTIFY INDEFINITE INCARCERATION. COURTS HAVE ALSO HELD THAT A PSYCHOLOGICAL DISORDER ALONE IS NOT SUFFICIENT FOR COMMITMENT, EVEN THOUGH A PSYCHOLOGICALLY DISORDERED INDIVIDUAL MAY BE IN NEED OF TREATMENT. ONLY IF SEXUAL OFFENDERS ARE JUDGED LIKELY TO REPEAT THEIR CRIME, WITH A SUBSTANTIAL RISK OF HARM TO VICTIMS, IS INDEFINITE COMMITMENT PERMISSIBLE AS A FORM OF PREVENTIVE DETENTION. IT IS CONCLUDED THAT ABOUT 15 PERCENT OF DANGEROUS SEXUAL OFFENDERS ARE NOT RESPONSIVE TO ANY AVAILABLE TREATMENT PROCEDURES AND THAT TREATMENT HAS A MODEST EFFECT FOR ABOUT 20 TO 25 PERCENT. FOR THE REMAINING OFFENDERS, A TOTAL TREATMENT EFFORT INVOLVING INDIVIDUAL AND GROUP PSYCHOTHERAPY, SOCIALIZATION EXPERIENCES, OCCUPATIONAL AND RECREATIONAL THERAPY, PRERELEASE PLANNING, AND POSTRELEASE TREATMENT AND SUPPORTIVE CARE HAS A PROFOUND EFFECT ON THEIR LIVES AND ON SUCCESSFUL SOCIETAL ADAPTATION. CLINICAL EVALUATION PROCEDURES FOR PREDICTING DANGEROUSNESS ARE DESCRIBED, AND CLINICAL PREDICTION STUDIES ARE REVIEWED. CLINICAL CRITERIA FOR DIAGNOSING DANGEROUSNESS AND THE ROLE OF THE CLINICIAN IN THE CRIMINAL JUSTICE SYSTEM ARE EXAMINED. (DEP)