Inflammation of the gastric and duodenal mucosa is the end result of an imbalance between mucosal defensive and aggressive factors. The degree of inflammation and imbalance between defensive and aggressive factors can then result in varying degrees of gastritis and/or mucosal ulceration. Gastritis and ulcers of the duodenum or stomach can be classified as primary or secondary. The majority of children with chronic gastritis and ulcers in the stomach or duodenum have secondary inflammation or mucosal ulceration. These secondary ulcers generally occur due to a systemic condition like head trauma or overwhelming sepsis, or as sequelae to drug ingestion (i.e. non-steroidal anti-inflammatory agents), but secondary gastroduodenal ulcers can also occur in specific disease conditions such as Zollinger-Ellison syndrome or Crohn's disease. In almost all children with primary duodenal or gastric ulcers mucosal inflammation and, less frequently, ulceration is caused by a spiral shaped, gram-negative, microaerobic rod Helicobacter pylori. Recent epidemiological evidence has linked chronic H. pylori infection with the development of gastric carcinomas.