Eosinophilic esophagitis is a chronic, immune-mediated disorder, isolated to the esophagus. Current theory suggests that the former may be caused by cell-mediated food hypersensitivity or may be a subset of eosinophilic gastrointestinal disease, an autoimmune disorder. During the last decade, the increasing prevalence of EoE has been recognized in pediatric populations. Reports support the efficacy of dietary restriction or corticosteroid therapy. Aditional research is needed to determine etiology, allow earlier clinical recognition and improve treatment. Because no single symptom, endoscopic finding or histopathologic feature is pathognomonic, the diagnosis can frequently be challenging. The current article reviews the possible etiology, clinical presentation, diagnosis, and treatment of this disorder, which has been called not only allergic esophagitis (which may be the most important cause), but also eosinophilic esophagitis, primary eosinophilic esophagitis, and idiopathic eosinophilic esophagitis.