The concept of endophenotypes has attracted considerable interest in psychiatry. It is thought that endophenotypes might be more closely related to the underlying biological processes and the genetic basis that give rise to a particular disorder than the relatively crude diagnostic categories defined in our conventional classificatory systems. In order to qualify as an endophenotype a characteristic has to be measurable and heritable, cosegregates with the illness, is state independent, is observed in unaffected family members and is a biologically plausible causal mechanism. In the field of eating disorders the study of endophenotypes is still in its infancy. The aims of this paper are to:

1. a. give an introduction to the concept of endophenotypes and its criticism,

2. b. review what is known about endophenotypes in eating disorders, and

3. c. present recent data from our own recent work on putative social cognitive endophenotypes.

Based on a review of the literature and our own research findings a handful of different temperamental and personality traits, neurocognitive and social characteristics can be identified that fulfill all the criteria to qualify as an endophenotypes. Other candidate endophenotypes need further study to ascertain whether they qualify.

The implications of this research for the classification of eating disorders are potentially far reaching.