Autoimmune gastritis (AIG) is an organ specific inflammation of the gastric mucosa. The cause of the disease is the autoimmune destruction of parietal cells in the oxyntic mucosa (mucosa which produces hydrochloric acid) with following hypo or achlorhydria and low pepsinogen I levels in the blood and gastric juice. Patients with AIG can have various clinical manifestations. The most often manifestation of the disease is pernicious anaemia, as well as sideropenia, hypocalciemia, stomachache, dysmotility disorders, digestion disorders, various manifestations of hypovitaminosis B12 and others. AIG can be complicated with development of the indolent carcinoid type I with overproduction of chromogranin A, serotonin or histamin. It is necessary to think of the AIG in clinical practice, it needs the long term surveillance of these patients, to detect early the long term consequences, such as gastric cancer and carcinoids. Authors in the article submit the mechanisms of the origin, injury and follow biochemical changes in the AIG.