The description of Helicobacter pylori and an understanding of its pathogenetic significance has been one of the major breakthroughs in gastroenterology in the past decade. Because of the possible implications, a correct diagnosis of the infection is mandatory. Diagnostic techniques can be divided into invasive and non-invasive methods. The first require upper gastrointestinal endoscopy with a biopsy taken from the stomach. These biopsy specimens can be studied for the presence of H. pylori using several histological staining techniques, or culture. In addition, urease tests are possible. The non-invasive techniques do not require endoscopy. They comprise testing for the presence of antibodies against H. pylori in the patient's serum, or breath tests with 13C- or 14C-labelled urea. In experienced hands every test has good sensitivity and specificity, and the test to be applied depends on local preference and experience.