Eleven years has passed since the guideline of the Korean College of Helicobacter and Upper Gastrointestinal Research group for H. pylori infection was produced in 1998. During this period the research for H. pylori has much progressed that H. pylori is now regarded as the major cause of gastric cancer. The seroprevalence of H. pylori in Korea was found to be decreased especially below the age of 40s and in the area of Seoul-Gyeonggi province, and annual reinfection rate of H. pylori has decreased up to 2.94%. In the aspect of diagnostic tests of H. pylori the biopsy is recommended in the body instead of antrum in the subjects with atrophic gastritis and/or intestinal metaplasia for the modified Giemsa staining or Warthin Starry silver staining. The urea breath test is the test of choice to confirm eradication when follow-up endoscopy is not necessary. Definite indication for H. pylori eradication is early gastric cancer in addition to the previous indications of peptic ulcer including scar and Marginal zone B cell lymphoma (MALT type). Treatment is also recommended for the relatives of gastric cancer patient, unexplained iron deficiency anemia, and chronic idiopathic thrombocytopenic purpura. One or two week treatment of proton pump inhibitor (PPI) based triple therapy consisting of one PPI and two antibiotics, clarithromycin and amoxicillin, is recommended as the first line treatment regimen. In the case of treatment failure, one or two weeks of quadruple therapy (PPI+metronidazole+tetracycline+bismuth) is recommended. Herein, Korean College of Helicobacter and Upper Gastrointestinal Research proposes a diagnostic and treatment guideline based on currently available evidence.