OBJECTIVE: This study investigates the overall pattern and timing of medical diagnoses up to 10 years before an anorexia nervosa (AN) diagnosis and explores differences before and after AN diagnosis aiming to improve early detection. METHOD: In this nationwide population-based cohort study, we included all patients diagnosed with incident AN from 1987 to 2018 (n = 13,345) and a 1:10 age- and sex-matched general population comparison cohort, using Danish health registries. Using conditional logistic regression, we calculated odds ratios (ORs) of medical diagnoses up to 10 years before AN diagnosis. Additionally, we calculated crude and adjusted hazard ratios (aHRs) for risk of medical diagnoses after AN diagnosis using Cox proportional hazards model. RESULTS: AN was associated with increased odds of any medical diagnosis up to 10 years before AN diagnosis: OR 1.3 [95% CI 1.2-1.3] and the odds increased during the 12 months preceding AN diagnosis: OR 1.6 [95% CI 1.5-1.7]. The medical diagnoses associated with the highest odds up to 10 years prior AN were malnutrition: OR 5.0 [95% CI 4.0-6.3] anemia: OR 2.9 [95% CI 2.3-3.6], amenorrhea: OR 2.7 [95% CI 2.3-3.2], and irritable bowel syndrome: OR 2.1 [95% CI 1.9-2.4]. The pre-diagnosis pattern mirrored the post-diagnosis pattern. CONCLUSION: The similarity in diagnosis patterns before and after AN diagnosis suggests that many patients receive medical diagnoses for conditions potentially linked to AN-related restricted eating, malnutrition and progressive weight loss even years prior to a formal AN diagnosis. Identifying these early conditions may enable earlier AN diagnosis and improve treatment outcomes.