Esophagitis is a very common disorder. The etiology cna be highly variable and is not always clear from the biopsy. The main microscopic inflammatory lesions are located in the epithelium. They consist of an increase in inflammatory cells, either polymorphs or mononuclear cells, or both. They are associated with architectural mucosal changes. It is often difficult or impossible to distinguish reflux esophagitis from drug-induced or viral esophagitis. Yet some microscopic patterns are characteristic and provide information on the etiology of the lesions.