Whether a diagnosis of a mental disorder contributes to the risk of poorer correctional outcomes is controversial. This study aimed to clarify the extent to which mental and substance use disorders individually and in combination contribute to correctional outcomes in order to determine optimal treatment and promote public safety. Methods: Differences were examined between four groups of federal offenders in Canada (N=715): those with a mental disorder only, those with a substance use disorder only, those with co-occurring mental and substance use disorders, and those with no disorder. : Login at top right hand side of page using your SSSFT NHS Athens for full text. SSOTP - You can request a copy of this article by replying to this email. Please ensure you are clear which article you are requesting.