The group-based program provides offenders with a rationale for the role that cognitions play in their offending, educates and informs the offender about the impact of his offense on the victim, identifies offense- related thought distortions, and assists the offender in challenging and exploring his cognitive distortions. Starting in October 1989 with an incest group, a series of five offense-focused groups have been operating at Dartmoor within a multidisciplinary team format. Each of the offense groups has focused on a single offense type. Two sets of groups, one rapist and one pedophile group, were conducted in parallel starting in January and October 1990. This evaluation focuses on these groups. Each of the offenders completed a series of questionnaires before and after participating in the treatment. All groups completed questionnaires related to Attitudes Toward Women (Spence and Helmreich, 1972), Rape Myth Acceptance (Burt, 1980), and the sexual maladjustment and loss of sexual control scales from the Thorne Sexual Inventory (Thorne, 1966). Additionally, a questionnaire related to the offenders' view of their offense was administered. The evaluation found encouraging evidence that offense-focused treatment groups are achieving their goals of changing the offender's perception of his offense behavior and the impact that it had on the victim in the expected prosocial direction. 2 tables and 12 references