The enormous genus Trechus Clairville is distributed mainly in the Holarctic regions, but 24 species from Ethiopia were described previously. A key to the species of Ethiopian Trechus is provided, including a new species, Trechus amharicus from the Choke Mountains (Ethiopian Highlands). The latter taxon is described. The species was found in the Afroalpine grassland, living under stones, sometimes located at the base of the giant Lobelia rhynchopetalum Hemsl. It is noteworthy that in spite of the small number of known species of Ethiopian Trechus, there are more morphological and chaetotaxic variations among them than in their Holarctic congeners. The taxonomic position of the new species is difficult to situate, because T. amharicus does not fit in any of the groups of species recognized to date in Ethiopia. T. amharicus n. sp. bears some resemblance to T. patrizii in that it has a pronotum with posterior angles without setae, and elytra with only a single anterior discal seta. However, the different configuration of the protarsus and aedeagus in the male clearly separates the two taxa.