In order to measure progress in sexual offender treatment programs, it is necessary to utilize measurement instruments that can reliably measure within-treatment changes. Practitioners have identified offender accountability as a central goal of most sexual offender treatment programs. As such, this study evaluated the ability of the FoSOD to reveal treatment progress by measuring changes in offenders’ willingness to take responsibility for their offense. A central research question was whether FoSOD can do more than distinguish between groups of offenders who may have scored differently in levels of denial independent of any treatment program. The FoSOD scores of 53 child molesters who were participating in a court-sanctioned sexual offender treatment program were measured 2 times over an 18-month interval to assess whether progress in treatment could be linked to changes in FoSOD scores. The authors hypothesized that FoSOD scores should decline as offenders progress through treatment. Results of statistical analyses supported the hypothesis; declines in FoSOD scores corresponded to advancement in treatment. Moreover, reductions in the various dimensions of denial continued to be detected even following a willingness to take accountability for the crime. However, FoSOD scores changed little for offenders who did not progress in treatment. The findings indicate the sensitivity of FoSOD in measuring treatment changes. The FoSOD also demonstrated the ability to differentiate between three components of denial: refutation, minimization, and depersonalization of the offense. The analysis indicated that the FoSOD avoids the typical challenges associated with self-report measures, including issues of validity and reliability, social desirability, and ambiguity about the appropriate application of measures. The use of FoSOD is thus encouraged as it allows clinicians to assess and target cognitive processes associated with offender treatment. Tables, figures, references