Although evidence is emerging that enhanced thinking skills (ETS) interventions are effective in reducing recidivism in prisoners, there is limited evidence supporting the effectiveness of ETS improving behaviour and functioning in prisoners with antisocial personality disorder (ASPD) traits. This study investigated the effectiveness of a group ETS programme in improving antisocial attitudes, anger regulation and social problem-solving skills in offenders with traits diagnostic of ASPD. A controlled trial was conducted comparing ETS programme with treatment as usual (TAU). Outcome measures were the Antisocial Personality Questionnaire, the Novaco Anger Scale and the Social Problem-Solving Inventory-Short Form. Significant improvements in the ETS group on all of the outcome measures were evident, when compared to TAU group. This study provides evidence that cognitive skills programmes based on ETS improve functioning in offenders with traits diagnostic of ASPD. The ETS programmes may be a therapeutic option when working with this historically difficult to treat group. However, further research is required that includes a randomised design, more objective behavioural outcome measures and a longer follow-up period.