A 1957 MASSUCHUSETTS LAW PROVIDED FOR THE CREATION OF TREATMENT CENTERS TO HANDLE OFFENDERS DEEMED 'SEXUALLY DANGEROUS,' I.E., THOSE WHO ARE SERIOUSLY SEXUALLY DISTURBED AND WHO REPRESENT A SIGNIFICANT THREAT TO SOCIETY. BETWEEN 1958 AND 1971, 240 MEN WERE COMMITTED TO THE CSENTER; 73 PERCENT HAD A PRIOR RECORD FOR A SEXUAL CRIME, AND 47 PERCENT OF THE OFFENSES IN QUESTION INVOLVED FORCE OR VIOLENCE. EXTENSIVE CLINICAL STUDY COMPRISING DIAGNOSTIC AND PSYCHOTHERAPEUTIC INTERVIEWS AND PSYCHOLOGICAL TESTS WAS CONDUCTED ON THESE PATIENTS. THIS ARTICLE IS A SYNTHESIS OF INFORMATION COMPILED IN FOUR RESEACH STUDIES MADE OF THE CLINICAL OBSERVATIONS. THE THREE CLASSES OF RAPE DIFFERENTIATED IN THE PAPER ARE: (1) AGGRESSIVE AIM, IN WHICH SEXUAL ASSAULT IS PRIMARILY AN AGGRESSIVE, DESTRUCTIVE ACT; (2) SEXUAL AIM, IN WHICH THE ACT OF RAPE IS CLEARLY MOTIVATED BY SEXUAL WISHES, AND AGGRESSION IS PRIMARILY IN THE SERVICE OF THIS AIM; AND (3) SEX-AGGRESSION DIFFUSION, IN WHICH SEXUAL EXCITATION IS USUALLY NOT EXPERIENCED WITHOUT SOME DEGREE OF VIOLENCE PRESENT. CLINICAL CASE HISTORIES TO ILLUSTRATE EACH CATEGORY ARE INCLUDED. THE SEX-AGGRESSION GROUP EXHIBITS PARANOID FEATURES, WHILE SUCH QUALITIES ARE NEARLY ABSENT IN THE SEXUAL AIM GROUP. SEXUAL PERVERSIONS ARE MORE COMMON IN SEXUAL AIM RAPISTS, AND EXCESSIVE DEFENSES AGAINST HOMOSEXUALITY THROUGH EXCESSIVE MASCULINITY ARE PREDOMINANT IN THE AGGRESSIVE AIM PATIENTS. LITTLE SUCCESS HAS BEEN ACHIEVED WITH THE SEX-AGGRESSION GROUP; THIS CLASS ALSO REPRESENTS THE GREATES RISK OF MALADAPTIVE BEHAVIOR. THE AUTHORS CONTEND THAT, BASED ON THE LIFELONG PATHOLOGICAL RELATIONSHIPS WITH WOMEN SEEN IN THESE THREE GROUPS OF RAPISTS, THERE IS NO REASON TO BELIEVE THAT A PRISON SENTENCE WILL MAKE THEM LESS DANGEROUS. ALTHOUGH BOTH THE MASSACHUSETTS LAW AND THE TREATMENT CENTER HAVE COME UNDER CRITICISM, SOCIETY DOES HAVE A RIGHT TO PROTECT ITSELF FROM SUCH VIOLENCE. REFERENCES ARE PROVIDED.