BACKGROUND: Eosinophilic gastritis and/or eosinophilic duodenitis (EG/EoD) is characterized by persistent symptoms and elevated eosinophils in the gastrointestinal tract. Limited disease awareness and lack of diagnostic guidelines suggest that patients may remain undiagnosed or endure diagnostic delay. OBJECTIVE: To characterize the path to diagnosis for patients with EG/EoD in a representative population. METHODS: In this observational cohort study, 4108 eligible patients diagnosed with EG/EoD between 2008 and 2018 were identified in an administrative claims database in the United States. Patient medical claim history was analyzed to describe events related to diagnosis. RESULTS: Mean year from symptom presentation to diagnosis of EG/EoD was 3.6; factors contributing to diagnostic delay included delayed gastroenterologist referral, delayed esophagogastroduodenoscopy (EGD), and lack of biopsy collection and/or histopathologic evaluation. Missed diagnosis on index EGD occurred in 38.2% of patients, resulting in a mean increase of 1.6 years in time to diagnosis versus patients diagnosed on index EGD. Patients presented with nonspecific symptoms and 44.3% were diagnosed with another gastrointestinal condition before EG/EoD diagnosis. Independent predictors of >2-year diagnostic delay included adult age; prior diagnosis of irritable bowel syndrome, functional dyspepsia, or gastric/peptic ulcer; use of other procedures such as colonoscopy; presence of edema; and history of certain allergic diseases. CONCLUSIONS: This study found that patients with EG/EoD experienced an average of 3.6 years between initial symptom presentation and diagnosis and revealed several factors contributing to diagnostic delay. We hope that these findings, together with heightened awareness and standardization of diagnostic guidelines, will improve the diagnostic journey of patients with EG/EoD.