The use of psychological interventions within medical contexts is a relatively new field. The adaptation of cognitive therapy for use in this context holds promise. However, at present the lack of a generalized cognitive model of illness behaviour is a restriction to further development. Recently developed social cognitive models of ‘normal’ illness behaviour may also be able to offer some insights into dysfunctional illness behaviour. Self‐regulation theory (Leventhal, Meyer & Nerenz, 1980) and existing cognitive models of chronic pain and health anxiety are reviewed and a new cognitive model of dysfunctional illness behaviour is proposed. A central role is given to the patient's beliefs about their illness, other beliefs, particularly about self, others and the world, and the net interaction of these two sets of beliefs which give the illness its own unique meaning for that individual. These three components are described as the illness belief triad. The model leads to specific suggestions for the clinical assessment and treatment of dysfunctional illness behaviours using cognitive behavioural interventions.