Her Majesty's Prison Service operates treatment programs for sexual offenders in 26 prisons in England and Wales. All of the programs operate under the same treatment manual, which provides detailed instructions on procedures for group cognitive behavioral treatment. Each session in each program in each prison has been videotaped since treatment programs began in 1991. Researchers obtained 12 2-hour videotapes from 7 prisons. Although the researchers requested that the seven programs selected show significant variability in treatment benefits, the videotapes sent to researchers showed similar, moderate improvements on most benefit measures. Despite this circumstance, evaluators of the videotaped therapist styles did show some significant links between therapist styles and changes in clients as a result of treatment. Twenty-eight features of therapists' styles were assessed on each of the videotapes and compared with treatment benefits determined from pretreatment and posttreatment evaluations of participants. Two sets of therapist features were quite influential. The first set included empathy, warmth, "rewardingness," and "directiveness." These therapist features were all positively related to beneficial change in clients. The other set of therapist features consisted of confrontation (harsh approach to challenging clients likely to be perceived by clients as denigrating) and nonconfrontation (firm but supportive challenges). Confrontation was related to poor outcomes, and nonconfrontation was linked to beneficial treatment outcomes. 2 tables and 15 references