This paper reviews the characteristics of clinical perfectionism and proposes a new definition of the phenomenon. It is suggested that the defining feature of clinically significant perfectionism is the overdependence of self-evaluation on the determined pursuit (and achievement) of self-imposed personally demanding standards of performance in at least one salient domain, despite the occurrence of adverse consequences. It is suggested that such clinical perfectionism is maintained by the biased evaluation of the pursuit and achievement of personally demanding standards. Specifically, it is suggested that people with perfectionism react to failure to meet their standards with self-criticism. If they do meet their standards, the standards are re-evaluated as being insufficiently demanding. Anorexia nervosa and bulimia nervosa are considered to have a particular relationship to perfectionism, with both disorders often being direct expressions of perfectionism. Under these circumstances self-evaluation is dependent on the pursuit and attainment of personally demanding standards in the domain of control over eating, shape and weight. The implications of this analysis for research and practice are considered.