Lophophora diffusa (Cactaceae) –an endangered species– known as peyote or peyote queretano– is of great ecological relevance because of its medicinal and ornamental use by native peoples and collectors. Little is known about the population of this species and no strategies exist for their use since its cultivation and usage is prohibited in Mexico. Thus, the objective of the present research is to describe population dynamics in a locality of the state of Querétaro, México. For this purpose, 380 individuals were followed through four annual and one quinquennial censuses. From these data, the population structure was determined, including the finite population growth rate (λ), stable size structure, reproductive value, relative importance of size categories and demographic processes (permanence, growth, and fecundity) for each period by using transition matrixes. Moreover, future population estimations were performed, showing scarcity of seedlings and adult plants of greater size, where λ indicates a population decline that oscillates between 2 and 20%. The most important demographic process was survival, where the adult 2 category resulted essential. The projections indicate that the population may disappear in a period of less than 50 years. Therefore, the proposal is to revise the Mexican legislation to allow a regulated cultivation with the purpose of protecting the wild populations of the species and its habitat.