Several reports of estimates for precancerous conditions for gastric adenocarcinoma can be found in the current literature. Our aim was to systematically review and estimate the prevalence of gastric precancerous conditions. Four databases (PubMed, Scopus, Web of Knowledge and EBSCO Academic Search Complete) were searched for original manuscripts addressing the presence of chronic atrophic gastritis (CAG) or intestinal metaplasia (IM). Subgroup analysis was carried out on methods of diagnosis, type of population, incidence of gastric cancer, sex, Helicobacter pylori status, age and extent of conditions. Overall, 107 studies were included. The worldwide prevalence of CAG in the general population was 33% (95% confidence interval: 26-41%) when considering biopsies (n=20 912) and 24% (19-29%) if serology (n=51 886) was used, whereas IM was found in 25% (19-30%) (n=30 960). Estimates for CAG were higher in countries with a high incidence of gastric cancer (42 vs. 23%), men (32 vs. 28%), H. pylori positive (46 vs. 17%) and if aged 40 years or older (48 vs. 22%). The prevalence of extensive conditions was 16% (12-20%) for CAG and 13% (9.0-17%) for IM. When comparing countries with high versus low to moderate incidence of gastric cancer, significant differences were achieved for CAG: 27% (12-36%) versus 7.3% (5.6-9.0%). Worldwide, one-third and one-fourth of individuals may harbour CAG and IM, respectively. In countries with a high incidence of gastric cancer, the prevalence of extensive conditions may increase up to 27% and these patients represent a high-risk population to whom endoscopic surveillance should be offered according to recent guidelines.