Comorbidity and dual diagnosis have a fashionable, and thus ephemeral, ring that belies their relevance to day-to-day practice. The topic has been increasingly addressed in North American literature where there is a recognition of the extent of substance misuse in the severely mentally ill, and the need to find ways of effectively managing its consequences. Substance misuse may colour the diagnosis, management and prognosis of major mental illness and can adversely affect the relationship between staff and patients. Despite its common occurrence, it frequently remains undetected (Ananth et al, 1989). With burgeoning research interest, there is some consensus as to how to manage the problem, but, as yet, little agreement on the precise nature of causal relationships.