The hypothesis of the study is that low-cost self-completion questionnaires relating to eating disorder symptoms will predict the subsequent results of a detailed, semi-structured interview assessment of eating disorder symptoms that has been calibrated according to expert clinical diagnostic case thresholds. Eating disorders are recognised as a research priority among healthcare professionals, adults with lived experience, and their carers alike. There is a need for measurement methods that can reliably and systematically identify symptoms of common forms of eating disorder, including those fulfilling agreed diagnostic criteria for anorexia nervosa, bulimia nervosa, and binge-eating disorder. Effective diagnostic interview tools can facilitate early detection of eating disorders. To develop rules for determining whether diagnostic criteria for eating disorders are met, a study involving adults referred to specialist eating disorder services is required. In this study, assessments by eating disorder clinicians will be compared with researcher assessments using a semi-structured interview assessment, the Schedules for Clinical Assessment in Neuropsychiatry version 3 section 9 (SCANv3s9). The study population will consist of 100 adult patients referred to specialist eating disorder services, including patients whose referrals are accepted by these services, as well as those who are not. Clinical assessments and structured interview assessment findings will also be compared with those from widely used screening tools for eating disorders, the Eating Disorder Examination Questionnaire short-form and the SCOFF (Sick, Control, One, Fat, Food) questionnaire. The aim of this study is to evaluate the accuracy of the Eating Disorder Examination Questionnaire Short-Form (EDE-QS) and the SCOFF (Sick, Control, One, Fat, Food) questionnaire in adults referred to specialist eating disorder services, in a comparison with the Schedules for Clinical Assessment in Neuropsychiatry subsection on eating disorders and specialist NHS clinician assessments of the probability of eating disorder. This will help develop appropriate and accurate benchmarks for estimating the prevalence of eating disorder symptoms and clinical diagnoses, in adults referred to specialist eating disorder services, as well as the wider population (through combining the findings from this study with those of the community 2023 Adult Psychiatric Morbidity Survey).