The genus Trichocereus is represented by 19 taxa (12 species, 5 subspecies and 2 varieties) in Chile, 13 of them endemic to this country. These occur from the regions of Arica and Parinacota on the border with Peru, to the region of Maule, the IV Region of Coquimbo presenting the highest taxonomic richness. Its species are a dominant feature of the landscape and define phytogeographic regions. This taxonomic study has yielded iconographies, original descriptions, detailed descriptions, taxonomic comments, information on distribution and habitat, exsiccata, nomenclature, and three keys for the identification of species, subspecies and varieties. This treatment provides an updated synonymy including eight new synonyms; a new combination, Eulychnia coquimbana (Molina) S. Albesiano; three taxonomic level changes: (1) Trichocereus chiloensis subsp. australis (F. Ritter) S. Albesiano, (2) Trichocereus chiloensis subsp. eburneus (Phil. ex K. Schum.) S. Albesiano, and (3) Trichocereus chiloensis subsp. panhoplites (K. Schum.) S. Albesiano; three new names: (1) Trichocereus faundezii S. Albesiano, (2) Trichocereus pectiniferus S. Albesiano, (3) Trichocereus undulosus S. Albesiano; and thirteen neotypifications.