Background: Research on which specific maladaptive cognitions characterize eating disorders (ED) is lacking. This study explores irrational beliefs (IBs) in ED patients and controls and the association between IBs and ED-specific and non-specific ED symptomatology and cognitive reappraisal. Methods: 79 ED outpatients with anorexia nervosa, bulimia nervosa, or other specified feeding or eating disorders and 95 controls completed the Attitudes and Beliefs Scale-2 (ABS-2) for IBs. ED outpatients also completed the Eating Disorder Inventory-3 (EDI-3) for ED-specific (EDI-3-ED Risk) and non-specific (EDI-3-General Psychological Maladjustment) symptomatology; General Health Questionnaire (GHQ) for general psychopathology; Emotion Regulation Questionnaire (ERQ) for cognitive reappraisal. Results: Multivariate analysis of variance with post hoc comparisons showed that ED outpatients exhibit greater ABS-2-Awfulizing, ABS-2-Negative Global Evaluations, and ABS-2-Low Frustration Tolerance than controls. No differences emerged between ED diagnoses. According to stepwise linear regression analyses, body mass index (BMI) and ABS-2-Awfulizing predicted greater EDI-3-ED Risk, while ABS-2-Negative Global Evaluations and GHQ predicted greater EDI-3-General Psychological Maladjustment and lower ERQ-Cognitive Reappraisal. Conclusion: Awfulizing and negative global evaluation contribute to better explaining ED-specific and non-specific ED symptoms and cognitive reappraisal. Therefore, including them, together with BMI and general psychopathology, when assessing ED patients and planning cognitive–behavioral treatment is warranted.