We describe the diagnosis and treatment of a patient with autism spectrum disorder (ASD) and substance use disorder (SUD). The patient had been given the dual diagnosis of Asperger’s disorder and SUD. On that basis the approach adopted and the treatment provided seemed appropriate. Little is known about the comorbidity of ASD and SUD and it has hardly been reported in the scientific literature or in clinical practice. Epidemiological research shows that this dual diagnosis occurs in clinical populations. A careful psychiatric diagnosis is important in order to ensure that the comorbidity is recognised at an early stage and treated in an appropriate manner.