The programs included both prison-based and non-prison-based programs. The studies were all completed in the last 10 years, although the treatment sometimes occurred earlier. The research examined elements of the research design to determine the study's internal validity and then gave each study a score for methodological rigor. The research then formed general conclusions about what works, what does not work, what is promising, and what is not known. Eight of the studies were deemed too low in scientific merit to include in assessing treatment effectiveness. Approximately 50 percent of the remaining studies revealed statistically significant findings in favor of sex offender treatment programs. Four of the six studies that indicated a positive treatment effect incorporated a cognitive-behavioral approach. Results indicated that non-prison-based sex offender treatment programs were effective in curtailing future criminal activity and that prison-based programs were promising, but the findings were not strong enough to support a conclusion that such programs are effective. Finally, too few studies focused on particular types of sex offenders to permit any type of conclusions about the effectiveness of programs for different types of sex offenders. Tables, notes, and 28 references (Author abstract modified)