BACKGROUND: Adult-onset food protein -induced enteroco-litis syndrome (FPIES) has been increasingly recognized in recent years. Adult FPIES differs from pediatric FPIES in terms of dietary triggers and symptoms, thus further broadening the clinical phenotypes of the disease. The natural history of FPIES in adulthood is poorly characterized.OBJECTIVE: To evaluate the natural course of FPIES in adults.METHODS: We performed an ambispective study of adults diagnosed with acute FPIES during 2016-2021. Data on age, sex, symptoms, implicated food, and oral food challenge (OFC) outcomes at baseline and during follow-up were analyzed.RESULTS: Forty-two adults were included (83.3% female; median age at diagnosis, 40 years). The predominant symptoms were diarrhea (92.9%) and abdominal cramps (71.4%); vomiting was reported by 59% of patients. The most common triggers were shellfish (n = 19, 45.2%) and fish (n = 19, 45.2%). The mean number of reactions before diagnosis was 6.3 (2-15). Twenty-one OFCs were carried out with the offending food in 15 patients. Six patients achieved tolerance (40%) after a mean of 17.8 months (range, 6-36 months). Twelve of all OFCs performed were positive (57.1%). The absolute leukocyte and neutrophil counts measured before and 1 to 2 hours after the positive challenge showed a mean increase of 3045 and 2736 cells/mL, respectively. Serum tryptase, C-reactive protein, and eosinophil and platelet values did not change significantly after the OFC.CONCLUSION: Some patients may outgrow adult-onset FPIES. (c) 2022 American Academy of Allergy, Asthma & Immunology (J Allergy Clin Immunol Pract 2022;10:2986-92)