This article discusses the behavioural attitudes of high expressed emotion as a major contributor to relapse in patients dually diagnosed with severe mental illness and substance use disorder. There are a number of research studies and authoritative texts on this particular problem and discussions identify the role expressed emotion plays in this condition. However, the majority of literature concentrates on how high expressed emotion affects the person's mental illness causing relapse rather than any effect on their substance misuse. This article outlines severe mental illness and substance use disorder; identifies the components of expressed emotion and how this may contribute to relapse; management and care in this condition; the treatment and avoidance of expressed emotion by the family and the professional; and issues of nurse education, training and support.