Compliance is adherence to a prescribed and appropriate treatment, not necessarily pharmacological. Non-compliance may occur in up to 50% of patients with schizophrenia who are prescribed neuroleptics. It may be commoner in young people, particularly if male or from certain ethnic minority groups, but demographic factors are relatively unimportant. Clinical features such as positive symptoms are associated with non-compliance but the strongest clinical relationship is with a "dual diagnosis", usually with an associated alcohol abuse. Patients' and relatives' beliefs about schizophrenia and about medication are of considerable importance in determining compliance, and can be understood in terms of the "health belief model". However, a full understanding of non-compliance must take into account the relationship between patients and doctors in the context of the sick role. Several techniques for increasing compliance have been described, but they contain common elements--the provision of information within the context of a warm and equitable therapeutic relationship, preferably maintained over some time, and the use of the relationship to encourage and prompt compliance and to establish more productive views of the illness and medication. The costs of poor compliance to sufferers and to society alike are considerable, and effective ways of improving it are a crucial part of good management.