This paper explores a possible connection between neurochemistry and cognitions in eating disorders (ED). Cognitions play an important role in ED. However, a possible neurochemical origin of these cognitions has not been explored. Obsessive-compulsive disorder (OCD) is known as a disorder of thinking. Extensive neurochemical research conducted on this disorder indicates a connection between serotonin (5-HT) dysregulation and cognitions in OCD. This study used research done on OCD as a template to interpret the available research findings in ED and their possible meaning in terms of neurochemical origin of cognitions in ED. This paper suggests that the neurochemical and behavioral expression of both ED and OCD occur on a continuum. At one end of the continuum, ED and OCD are expressed through constrained behaviors of an avoidant quality. This pole is also characterized by high levels of serotonin markers. At the other end, both disorders are characterized by disinhibited approach behavior. This end of the continuum is characterized by low levels of 5-HT markers. It is suggested that these levels of 5-HT generate cognitions that may in turn promote specific behaviors.