The finding of H pylori in the gastric mucosa has changed the understanding of the pathogenesis of common diseases of the stomach and duodenum. The bacteria causes acute and chronic gastritis and is the precursor of peptic ulcers, gastric lymphoma and gastric cancer. The most common test used to diagnose the infection is the urease test on a gastric biopsy but an endoscopy must be performed to obtain the biopsy. Determination of serum levels of IgG appears the most suitable test to perform in large population studies. Patients with peptic ulcers, gastric lymphoma and early gastric cancer should be treated. Combinations of antibiotics such as amoxicillin, chlaritromycin and a proton pump inhibitor have yielded the best results in erradicating H pylori. Unfortunately this therapy is expensive and new combinations should be explored. Vaccination should be the treatment of choice for prevention and erradication in countries like Chile with high infection rate. Preliminary results are encouraging.