Objective: To identify the type and proportion of depressive and related mental health disorders in a group of individuals seeking outpatient treatment at an alcohol and other drug (AOD) service. Design, setting and participants: A cross-sectional study using diagnostic interviews with 95 participants (56 men, 39 women) seeking treatment from an AOD service. Main outcome measures: Mental health and substance disorders were measured using the Composite International Diagnostic Interview, Posttraumatic Stress Disorder Checklist, Beck Depression Inventory, and State–Trait Anxiety Inventory (Trait Version). Results: This was a complex group with addiction, mental health and physical health conditions; 76% had a depressive disorder and 71% had an anxiety disorder. Most were diagnosed with at least two mental health disorders and 25% were diagnosed with four or more different disorders. Alcohol and cannabis use were the most commonly diagnosed AOD disorders. Further, those diagnosed with a drug use disorder reported significantly higher levels of depression compared with those with an alcohol-only disorder. Finally, 60% of the sample reported chronic health conditions, with over one-third taking medication for a physical condition on a regular basis. Conclusions: Primary care providers such as general practitioners are likely to be increasingly called on to assess, treat and/or coordinate care of patients with AOD disorders. We show that this group will likely present to their GP with more than one mental health disorder in addition to acute and chronic physical health conditions.