Body dysmorphic disorder (BDD) is the most distressing and handicapping of all the body image disorders. A cognitive behavioural model of BDD is discussed which incorporates evidence from recent studies and advances in the author's 1996 conceptual model. The model aims to understand the maintenance of symptoms in BDD, to assist in the process of engagement of therapy and to guide the strategies to use. At the core of BDD is an excessive self-focussed attention on a distorted body image, the negative appraisal of such images leading to rumination, changes in mood and the use of safety behaviours. Evidence for possible risk factors in the development of BDD is also discussed.