IN CANADA, PROPOSED DANGEROUS OFFENDER LEGISLATION WOULD PROVIDE FOR AN INDETERMINATE SENTENCE OF PREVENTIVE DETENTION FOR CERTAIN CLASSES OF OFFENDERS WHO, ON THE BASIS OF CLINICAL EVIDENCE, ARE JUDICIALLY DETERMINED TO CONSTITUTE A CONTINUING DANGER AND TO BE LIKELY TO ENDANGER THE SAFETY OF OTHERS. TWO PRINCIPAL METHODS OF DETERMINING THE DANGEROUSNESS OF OFFENDERS ARE REVIEWED. THE PSYCHIATRIC OR PSYCHOLOGICAL EVALUATION METHOD IS SHOWN TO BE EXTREMELY UNRELIABLE, WHILE PREDICTION THROUGH ACTUARIAL DEVICES SUCH AS PREDICTION TABLES IS ALSO SHOWN TO BE INACCURATE. THE AUTHOR MAINTAINS THAT THE PRESENT STATE OF EXPERTISE RESPECTING THE PREDICTION OF FUTURE DANGEROUSNESS IS INADEQUATE, AND THAT TO TAKE CONTROL OVER AN INDIVIDUAL'S LIFE ON THE BASIS OF SUCH IMPERFECT KNOWLEDGE IS UNJUST. HE CONCLUDES THAT A DANGEROUS OFFENDER STATUTE SHOULD NOT BE ENACTED. (AUTHOR ABSTRACT MODIFIED)