This study explored the impact of psychiatric and psychological treatment on hostile-dominance in 51 offenders with personality disorder in a secure psychiatric unit. Hostile-dominance was assessed at intake and repeated at six monthly intervals. In 28 of the participants with reassessment of hostile-dominance, who were subsequently discharged into the community, the association between reoffending (Grave and Any) and change in hostile-dominance (measured by subtracting the final hostile-dominance score from the initial score), psychopathic traits, Antisocial Personality Disorder (ASPD) and treatment completion/non-completion was examined. Results revealed that patients who completed treatment evidenced a reduction in hostile-dominance, whereas patients who did not complete treatment worsened. Logistic regression analyses showed that reduced hostile-dominance, psychopathy and ASPD predicted reoffending (Any). Treatment completion and Psychopathy Checklist Factor 1 scores predicted Grave reoffending. Findings are supportive of the potential for the level of hostile-dominance to be reduced through completion of appropriate treatment; such changes are important to reductions in reoffending.