his thesis considers personality disorder (PD) within a forensic population. The first chapter is comprised of a systematic literature review of the association between specific offence typologies and specific PDs. Antisocial and narcissistic PD were more prevalent in non-sexual groups, whilst avoidant, schizoid and borderline PD were more prevalent in sexual offenders. However, heterogeneity in the methodologies of included studies meant that robust conclusions could not be drawn. A narrower research question was recommended, along with more comparable studies. The second chapter explores PD within a therapeutic community prison. PD, identified by the Personality Diagnostic Questionnaire (PDQ) (Hyler, 1994) was highly prevalent in this sample (86.2%). Intervention was found to be effective in reducing disordered personality traits, such as psychoticism, impulsivity and hostility. Further to this, clinically significant change in personality traits showed a difference between clusters. For example, criminality reduced significantly within cluster B disorders. This research demonstrated the effective treatment of PD offenders within a therapeutic community, but further research is required before robust conclusions can be drawn. Finally, the findings from the thesis were placed in the context of the critique of the PDQ. Findings suggested the PDQ has a tendency to over-diagnose PD. However, the challenges faced in diagnosing PD per se and limitations of the current diagnostic criteria were discussed. Overall, the thesis raises some interesting findings into the effectiveness of a therapeutic community prison with PD offenders. This may be beneficial to guide future research in the area and the development of effective interventions with such a population.