Those living in Northwestern Ontario are at a heightened risk for mental health disorders. Mental health symptoms can be exacerbated when an individual is suffering with co-morbid substance use difficulties. Treating co-morbid mental health and substance use difficulties is often a challenge in a clinical setting. Dialectical Behaviour Therapy (DBT) is empirically validated as a treatment for both mental health and substance use difficulties. This study provides an evaluation of the St. Joseph’s Care Group (SJCG) Mental Health and Addictions DBT program. Specially, examining how effective it is at treating people with co-morbid mental health and substance use difficulties. The sample included 44 outpatient clients who were referred to the DBT program from one of the affiliated SJCG programs. The program is intended for adult outpatients only. Each participant was given a questionnaire aimed at measuring mental health symptoms, quality of life, as well as adaptive and maladaptive coping behaviours. Participants completed the same questionnaire at intake, as well as 6 and 12 months into treatment. Change in symptoms, quality of life, and coping behaviours was analyzed using the SPSS-25 software. The DBT program resulted in: Improved quality of life, reduced mental health symptomology, as well as reduced dysfunctional coping strategies. Clients also experienced a reduction in problematic behaviours (i.e., drug use, self-harm, alcohol abuse). Further, clients who continued treatment for 12 months experienced a continual improvement in most areas and demonstrated better end-of-treatment scores than those who completed treatment at 6 months. Results from this evaluation suggest that DBT contributes to improvements in multiple aspects of functioning for the clients receiving this service.