Primary care physicians encounter many patients with primary and secondary anxiety and substance use problems. Some patients have a dual diagnosis of both an anxiety and a substance use disorder. Symptoms may be overdiagnosed, underdiagnosed, and misdiagnosed. This article provides the primary care physician with an overview of the relation between psychoactive substance use disorders and anxiety symptoms. Also described are drug use patterns and diagnostic criteria for psychoactive substance use disorders. A model for understanding the role of anxiety symptoms during drug use is provided.