Low rates of compliance with medication pose a major challenge to the effective management of most chronic diseases, including asthma. The high medical and social costs of non-compliance, and the apparent lack of effective methods for dealing with it, has stimulated renewed interest in this complex issue. Two broad categories of non-compliance have been identified, namely unintentional (or 'accidental') and intentional (or 'deliberate'). Unintentional non-compliance may result from poor doctor-patient communication or a lack of ability to follow advice. Intentional non-compliance occurs when the patient knows what is required but decides not to follow this to some degree. Healthcare professionals need to be aware of the various issues affecting compliance in all patients. The reasons for non-compliance are many and varied, and include factors such as complexity of the treatment regimen, administration route, patient beliefs about therapy and other psychological factors. Improvement in patient compliance with therapy will require better doctor-patient communication, improved patient education, the tailoring of therapy to the individual and possible novel strategies such as offering feedback to the patients on their level of compliance.