There are many diseases where the cause is unknown and this makes a specific treatment difficult. In many cases all that can be achieved is amelioration of the illness. Peptic ulcer disease was one such condition no more that 20 years ago. The management was drastic--either an operation or life-long medication in order to reduce the acid secreted by the stomach. However, the cause of this condition was discovered in 1983. Although initially sceptical, the medical fraternity now almost universally endorse Helicobacter pylori as the cause of the majority of stomach ulcers. Peptic ulcers can now be cured by antibiotics. This is a major shift in medical practice. Continued investigations on Helicobacter pylori are bringing to light other possible associations with disease as well as delineating plausible biological mechanisms for disease pathogenesis.