["European Eating Disorders Review, EarlyView. ", "\nABSTRACT\n\nObjective\nBulimia nervosa and related syndromes (BN‐S) are clinically heterogeneous and complex disorders. Frequent comorbidity with anxiety disorders (ADs) and substance use disorders (SUDs) implicates inherent fear‐ and approach‐based tendencies in BN‐S. This study aimed to clarify how comorbid ADs and SUDs, along with fear‐ and approach‐based traits, influence the presentation and severity of BN‐S.\n\n\nMethod\nWomen (N = 399) with BN‐S (n = 321) or no history of eating disorders (n = 78) completed the Eating Disorder Examination, Structured Clinical Interview for DSM‐5 Disorders, Behavioural Inhibition System/Behavioural Activation System scales, and the Sensitivity to Punishment and Sensitivity to Reward Questionnaire.\n\n\nResults\nDiagnostic features, symptom frequencies, and eating pathology scores were not significantly affected by comorbidity with ADs or SUDs. Controlling for ADs, participants with BN‐S scored significantly higher than controls on fear‐based traits. Similarly, controlling for SUDs, individuals with BN‐S showed elevated sensitivity to reward. Finally, elevated fear‐ and approach‐based traits both contributed to elevated severity across a range of bulimic symptoms.\n\n\nConclusion\nFear‐ and approach‐based traits coexist in individuals with BN‐S and were associated with the same symptoms. Although BN‐S are currently placed within the Hierarchical Taxonomy of Psychopathology's internalising spectrum, findings indicate overlap with the externalising spectrum.\n\n"]