Comorbid substance use and mental health disorders are highly prevalent and increase the risk of various adverse outcomes. Yet, treatment for comorbid substance use and mental health disorders is scattered and varies considerably between countries and regions. Quality standards are principles and sets of rules that can serve as a statement of expected requirements. They can be developed by (inter)national bodies and contribute to identification of shared ethical principles, harmonisation of care and implementation of evidence-based interventions. While in recent decades there has been an increase in the availability of quality standards in healthcare, and despite some national and regional efforts, international quality standards for the treatment of comorbid substance use and mental health disorders are lacking. Consensus over the development of such standards by international organisations could contribute to improved care for patients with comorbid substance use and mental health disorders globally.