This study compared maladaptive core beliefs of eating-disordered groups (full and subthreshold syndrome) and healthy controls and investigated the association between eating disorder symptoms and core beliefs. Participants were compared on self-report measures of core beliefs (YSQ) and eating disorder psychopathology (BITE). Anorexia nervosa (AN; both subtypes) and bulimia nervosa (BN) patients had significantly more core beliefs than healthy controls. Binge eating disorder (BED) patients had intermediate scores between AN and BN on the one hand and healthy controls on the other hand. No correlation was found between core beliefs and frequency of binge eating. Frequency of vomiting, laxative misuse and fasting was positively associated with all domains of core beliefs. Patients with eating disorders have some core beliefs which are not directly related to eating, weight or shape. Frequency of purging and fasting behaviors is associated with more severe maladaptive core beliefs. Our data demonstrate the importance of identifying purging and fasting as significant clinical markers.