A wide variety of infectious, inflammatory, and other disorders affect the gastric mucosa in pediatric patients. The most common cause of gastritis in children is Helicobacter pylori infection, which is also responsible for the majority of duodenal ulcers. Acute erosive gastritis is most commonly the result of metabolic stress or drug or corrosive injury. Other major causes of gastritis include celiac disease, allergic disorders, and Crohn's disease. The distinctive clinical, endoscopic, and histologic features of these disorders are discussed.