The faunas of Newfoundland and Cape Breton include 217 leafhopper species, of which 24 are introduced and 65 are native, common to both islands. Newfoundland has 116 species, of which 86 are new provincial records and 2 are new nearctic records of introduced European species. Cape Breton has 172 species, of which 109 are new records for Nova Scotia. A species previously known as far north as Virginia was found in Cape Breton, 2 New England species were found as far north as Newfoundland, 2 high boreal species were found as far south as Cape Breton, and 42 species previously known from west of Maine were found as far east as Cape Breton. One new subspecies and 14 new species are described: Cosmotettix unica, Oncopsis minor terranovae and Typhlocyba (Edwardsiana) unicorn from Newfoundland, Colladonus balius, Cribrus micmac, and Typhlocyba (Zonocyba) hollandi from Cape Breton, Oncopsis speciosa from both islands, Erythroneura maritima and M. inundatus from the Gulf of St. Lawrence region, Limotettix (Ophiolix) schedia, Latalus (Jassargus) remotus and Macrosteles galeae from eastern bogs, and Empoasca volsella, E. zanclus and Kyboasca papyriferae from Cape Breton westward across Canada. Three new synonyms are created: Amphigonalia Young, 1977 = Neokolla Melichar, 1926, Scaphytopius sarissus Beirne, 1952 = S. cinnamoneus (Osborn, 1915), and Typhlocyba frigida Hamilton, 1983 = T. tersa Edwards, 1914. Three genera are reduced to subgenera: Jassargus Zachvatkin, 1953 in Latalus DeLong & Sleesman, 1929, Lemellus Oman, 1949 in Sorhoanus Ribaut, 1946, and Scleroracus Van Duzee, 1894 in Limotettix Sahlberg, 1871. New World species formerly placed in Agallia Curtis are transferred to Agalliota Oman. Oncopsis prairiana Hamilton, 1983 and its subspecies are made subspecies of O. minor (Fitch 1851). The composition of the faunas of the two islands is compared with those of adjacent areas of the mainland, and evidence is found for an offshore glacial refugium.