Helicobacter pylori (HP) are Gram-negative spiral bacteria which occur in the human stomach. The bacteria were cultured in vitro for the first time in 1983. It is suspected that the bacteria may cause chronic gastritis of type B and may also be a contributory cause of chronic ulceration and cancer of the stomach. The bacteria are accompanied by characteristic inflammatory changes in the gastric mucosa. The significance for gastritis, chronic ulceration, non-ulcer dyspepsia and carcinoma of the stomach is discussed. HP occurs in a great proportion of the population of the world and the frequency increases with age. The route of infection is unknown but faecal-oral infection is probable. Correlation between the presence of HP and the occurrence of symptoms is poor in the individual patient. The bacteria can be demonstrated histologically, cytologically, by culture, by the urease test, by the urease expiration test or serologically. The bacteria are sensitive for a series of antibiotics and bismuth but no effective treatment is known as the recurrence rate is high.