Sex offender outcome studies continue to produce mixed results. A common critique of these studies is their lack of methodological rigor. This study attempts to address this critique by adhering to the standards established by the Collaborative Outcome Data Committee (CODC) aimed at increasing the quality and confidence in outcome studies. We examined recidivism outcomes for a sample of formerly incarcerated sex offenders who participated in a state prison-based cognitive-behavioral-skills-based treatment program. We used propensity score analysis to compare treatment participants with a matched sample of non-participants. The final sample post-matching (n = 512) was observed for a minimum of 4 years and a maximum of 14 years. Using survival analysis, findings indicate that there were no differences in recidivism rates between treatment participants and non-participants in sexual or violent crimes. However, participants demonstrated significantly lower rates of recidivism for non-violent crimes. We discuss strengths, limitations of the study, and implications of these findings.