The gastric precancerous process is evaluated in 1788 participants in a gastroscopy survey in the population of Nariño, Colombia, which has one of the highest gastric cancer incidence rates on record. A detailed histological classification is used, and a hierarchical distribution of lesions is described with the main stages being gland neck hyperplasia, atrophy (gland loss), intestinal metaplasia and dysplasia. Acute inflammation was not found to be a specific stage in the sequence but rather a common finding in all stages of the precancerous spectrum. Indices of disease progression for the different steps are calculated and found to increase with gastric pH and nitrate and nitrite content of the gastric juice. The effects of high pH and nitrite content are intimately correlated. Relative risks of specific lesions, namely, hyperplasia, atrophy, metaplasia, and dysplasia, increase linearly with higher pH, nitrate, and nitrite values in the gastric juice. The severity of atrophy correlates with the prevalence of metaplasia, suggesting a sequential relationship between the described stages, a finding supported by all parameters examined. The model of progression described may serve as a basis for comparisons with populations at different levels of gastric cancer risk but it fails to provide information concerning the time required for each change, which should be provided by follow-up (cohort) studies.