We present the results of our investigations in the epidemiology of H. pylori infection in Peru during the last two decades. The prevalence of Helicobacter pylori infection in Lima is decreasing in people of middle and high socioeconomic status and continues stationary in people of low socioeconomic status. This decrease is similar in Peruvian and Japanese population in this city, and is associated to the decrease of the gastrointestinal diseases related to this bacterium: peptic ulcer and stomach adenocarcinoma. The infection is slightly greater in males and is acquired in early ages of life. Via oro-fecal and water contamination are probably the most important transmission ways. In our country, so far, there is no evidence to assure that some races have higher pre-disposition to acquire the infection. There are no differences in the infection by H. pylori among coast, mountain or jungle populations; and people who live in high altitudes have more atrophic chronic gastritis secondary to H. pylori infection than people who live at sea level.