Of the 30 Neotropical species of Brachymyrmex, 26 live in Argentina. This genus was originally proposed by G. Mayr to for the Argentinian B. patagonicus. Santschi published the only systematic revision presently available, but several species cannot be yet easily separated or named. In this paper we redescribe B. patagonicus - the type species of Brachymyrmex - as well as B. bruchi and B. oculatus. Descriptions and drawings of the main morphological characters of queens, males and workers are given. Analyzed specimens belong to the Collections in the Museo Argentino de Ciencias Naturales "Bernardino Rivadavia", Museo de La Plata, Argentina and the Naturhistorisches Museum Wien. New characters are used to differentiate species, mainly male head morphology and genitalia. Two new synonymies are proposed: B. patagonicus var. atratulus = B. patagonicus and B. bruchi var. rufipes = B. bruchi, as we do not consider that differences in worker body color justify subspecific separation. Lectotype is designated for B. oculatus.
