Eosinophilic gastroenteritis (EG) was first described over 50 years ago. Despite its long history, it remains an ill-defined and poorly understood entity. EG can present in a number of ways, none of which are exclusive to the disorder. EG has features of allergy and immune dysregulation but does not clearly fit into the category of allergic or immune disorder. While EG has been reported to affect all locations and layers of the gastrointestinal tract, the vast majority of reported cases have demonstrated mucosal involvement of the gastric antrum and small intestine in addition to disease activity of other locations of the gastrointestinal tract. Recently, several reports have identified a disease consisting of an isolated esophageal eosinophilia. Eosinophilic esophagitis (EE), also known as primary eosinophilic esophagitis or idiopathic eosinophilic esophagitis, occurs in adults and in children and represents a subset of EG with an isolated severe esophageal eosinophilia. Patients with EE present with symptoms similar to those of gastroesophageal reflux but are unresponsive to antireflux medication. Reports have demonstrated that patients with EE respond to either dietary restriction or corticosteroids.