Uroleucon is one of the largest genera of Macrosiphini, with 216 known species; it is one of the few genera of Aphidinae to have a diversification in South America, with 15 native species and 1 subspecies. Moreover, 7 introduced species have been recorded in South America. Five new species from Argentina are described herein: Uroleucon malarguense Ortego and Nieto Nafría, sp. nov., U. mendocinum Mier Durante and Ortego, sp. nov., U. patagonicum Nieto Nafría and Seco Fernández, sp. nov., U. payuniense Ortego and Nieto Nafría, sp. nov., and U. riojanum Nieto Nafría and Mier Durante, sp. nov. One Palearctic species, U. jaceae (Linnaeus), has been recorded for the first time in South America, and thus 28 species and 1 subspecies are now known from South America. Uroleucon essigi Carvalho and U. chilense (Essig) are recorded for the first time from Argentina, and 20 of these 29 taxa are known for this country. New morphological and bionomic data from some previously known species are given. Alate viviparous females of U. gochnatiae Delfino and oviparae and males of U. bereticum (Blanchard) and U. macolai (Blanchard) are described. A taxonomic discussion about native South American species of Uroleucon is given, and we include them at present in the subgenus Lambersius. A key is provided for the identification of apterous and alate viviparous females.