General practitioners (GPs) are in a unique position to detect and manage patients with co-morbid mental health and substance use disorders (dual diagnosis). It has been estimated that over 30% of patients presenting to general practice have a diagnosable mental disorder and 12% have dual diagnosis. Unfortunately, between 30 and 50% of these problems go undetected in general practice. Limited GP education and training in mental health may account for this deficit, with a little over 8% of GPs receiving any formal postgraduate training in mental health. Prior to developing an educational resource for GPs, the present study aimed to establish baseline estimates of GP treatment practices with patients who have dual diagnosis. Two GP division-wide surveys of screening, assessment and treatment for dual diagnosis were conducted one year apart. In addition, five GPs conducted a clinical audit of 508 patient consultations. Results indicate that without ongoing targeted interventions, patient management activities such as GP counselling, use of screening devices, referral to specialist services, coordination and use of EPC items are not likely to improve and are at risk of declining.