Specifically, the study sought to determine whether motivation to participate in the program had an impact on the reduction of cognitive distortions (CD's). Seven CD's were analyzed in pretreatment and posttreatment assessments; the treatment was considered effective for offenders who eliminated more than half of the CD's by the end of the program. The sample consisted of the sex offenders from six sex offender treatment programs in three prisons in England. Thirty-one offenders completed both pretreatment and posttreatment assessments from March 1997 until August 1998. The CD's used in the study were minimization or denial, justification, lack of empathy for victims, triggering factors, fantasies, behavior management, and grooming or planning. The pretreatment and posttreatment interviews were used to determine whether the offenders continued to display CD's upon completion of the treatment program. Additionally, the interviews yielded information about the offenders' levels of motivation to participate in the treatment program. In the pretreatment assessments, all offenders displayed each of the seven CD's to some degree. Treatment was successful in reducing at least 4 CD's for 22 of the 31 offenders. Offenders were still classified as exhibiting the CD if it was present to any extent, even if the strength of that particular CD was significantly reduced. The results showed comparable success rates for sex offenders with adult victims who were and were not motivated to change their offending behavior. Motivation did have an effect on offenders with child victims, although the reasons for this were unclear and should be explored with a larger sample of offenders. 4 tables, 3 notes, and 14 references