Dual diagnosis is one of several terms used to identify individuals diagnosed with a co-occurring mental disorder and substance use disorder. The existence of a dual diagnosis in adolescents is often associated with functional impairment in various life domains, causing physical health problems, relational conflicts, educational/vocational underachievement and legal problems. Dual diagnosis is difficult to treat and can result in tremendous economic burden on healthcare, education and justice systems. It is essential for clinicians caring for young people to be knowledgeable about dual diagnosis to ensure that it is identified early and treated. This article aims to provide an overview of dual diagnosis, increase its awareness and promote a realistic treatment approach.