The current study aimed to explore the relationships between attachment and childhood trauma on recidivism risk in a sample of Canadian offenders with mental disorder (OMDs). N = 56 OMDs completed the Adverse Childhood Experiences (ACE) questionnaire, a measure of adult attachment (Experiences in Close Relationships Scale), and interview to determine recidivism risk (Level of Service/Case Management Inventory; LS/CMI). The variables of interest had small to moderate correlations. Multivariable regression analysis found that ACE scores but not attachment insecurity were associated with LS/CMI scores. Mediation analyses demonstrated that ACE scores fully mediated the association between attachment anxiety and attachment avoidance and recidivism risk. Results demonstrate that as exposure to diverse ACEs increased so did the risk to recidivate and this exposure mediated the relationship between attachment insecurity and recidivism risk. This study highlights the necessity of addressing both attachment insecurity and the experience of ACE when providing psychiatric services to OMDs.