A sexual offender treatment program operated by the Correctional Service of Canada supported the conclusion that cognitive behavioral treatment can reduce sexual offense recidivism. The study compared 296 treated and 283 untreated offenders followed for a mean of 6 years after release. An untreated comparison subject was located for each treated offender on three dimensions: age at index offense, date of index offense and criminal history. Data were analyzed using tests of proportion, survival analysis and analysis of offender Criminal Career Profiles. Convictions for new sexual offenses among treated offenders were 14.5 percent versus 33.2 percent for untreated offenders. During the follow-up period, 48 percent of treated offenders remained out of prison compared to 28.3 percent of untreated offenders. Time series comparisons of treated and comparison samples also showed that treated men reoffended at significantly lower rates after 10 years. Treatment did not appear to affect the rate at which treated offenders committed new non-sexual crimes, emphasizing the need for sexual offender treatment programs to address non-sexual violence and general criminal recidivism. Tables, figures, references