The hypotheses tested were that denial is inversely related to engagement in group therapy; that denial is inversely related to treatment progress; and that engagement correlates with treatment progress. The study used Macgowan's (1997) definition of "engagement" as "a multidimensional contract involving seven dimensions: attending or completing group sessions (attendance), contributing verbally or by participating in group activities (contributing), showing support for the work of the leader (relating to workers), interacting with other group members (relating with others), adopting the group contract (contracting), working on their own problems (working on own problems), and helping other group members to work on their own problems (working on others' problems)." The DSM-III-R defines "denial" as "a defense mechanism in which the person fails to acknowledge some aspects of external reality that would be apparent to others." "Treatment progress" is defined as "active change and its maintenance." The findings of this study indicate a strong correlation between engagement in group therapy, measured by the Group Engagement Measure, and sex offender treatment progress, assessed with the Sex Offender Treatment Rating Scale. Denial, measured by the Facets of Sexual Offender Denial Scale, revealed a strong inverse relationship to treatment progress. Engagement and denial were also strongly inversely related. Combined, engagement and denial explained a significant amount of the variance in treatment progress. These findings support current standards of practice, which maintain that admitting to a sex crime is a necessary condition for progress and engagement in treatment. This paper suggests strategies for increasing engagement and treatment progress while reducing denial. 4 tables and 40 references