Background: Despite its uncommon occurrence, eosinophilic gastroenteritis is one of the most important primary eosinophilic gastrointestinal disorders. These are defined as disorders that selectively affect the gastrointestinal tract with eosinophil-rich inflammation in the absence of known causes for eosinophilia. The disorders include eosinophilic esophagitis, eosinophilic gastritis, eosinophilic gastroenteritis, eosinophilic enteritis and eosinophilic colitis. Aim of the study: This review focuses on the epidemiology, pathophysiology, clinical features and treatment of primary eosinophilic gastrointestinal disorders with particular attention to primary eosinophilic gastroenteritis. Clinical case: We report a case of a 32-years-old woman that was admitted to our Hospital complaining of abdominal pain, ascites and diarrhea. Laboratory investigations showed a white cell count of 15.1 thousands/mm3 with eosinophilia; other laboratory studies were within the normal limits. Abdominal ultrasonography demonstrated peritoneal effusion and cytological analysis revealed a prevalence of eosinophils in the ascites. The multiple endoscopic biopsies were normal. However, the clinical history, and the laboratory, radiological and endoscopic findings gave a firm diagnosis of the serosal form of primary eosinophilic gastroenteritis. Discussion: This is a rare, benign condition, pathologically characterized by an important eosinophilic infiltration of the wall of the digestive tract and presents a constellation of symptoms that are related to the degree and area of the gastrointestinal tract affected. Primary eosinophilic gastroenteritis encompasses multiple disease entities subcategorized into three types on the basis of the level of histologic involvement: mucosal, muscolaris and serosal forms. Every layer of the gastrointestinal tract can be involved, so that endoscopic biopsy can be normal in patients with the muscolaris subtype, serosal subtype, or both.