Co-morbidity of personality disorder and clinical syndrome in high-risk incarcerated offenders Abstract Purpose: In light of the clinical importance of understanding co-morbidity within offender populations, this study examined the prevalence and comorbidities of clinical disorder (Axis I) and personality disorder (Axis II) within a sample of high risk, male offenders located in a high secure, prison-based personality disorder treatment service. Methodology: The study utilised clinical assessment data for both Axis I diagnoses (Structured Clinical Interview for DSM-IV) and Axis II diagnoses (International Personality Disorder Examination) of personality disordered offenders (n=115) who met the criteria for the treatment service between 2004 and 2015. Findings: Co-morbidity between Axis I and Axis II diagnosis was high, with 81% of the sample having co-morbid personality disorder and clinical disorder diagnosis. The most prevalent Axis I disorder was substance misuse, and Axis II was anti-social, borderline, and paranoid personality disorder. Following Chi-square analysis, Cluster A personality disorder demonstrated co-morbidity with both mood disorder and schizophrenia/other psychotic disorder. Paranoid, schizoid, narcissistic, and avoidant personality disorder demonstrated a level of co-morbidity with Axis I disorders. There was no association found between the clinical disorders of substance use and anxiety with any personality disorder within this sample. Value: In part these results suggest that certain Axis II disorders may increase the risk of lifetime Axis I disorders. The findings of no co-morbidity between the clinical disorders of substance use and anxiety with any personality disorder within sample is inconsistent to previous findings.