Four virus diseases can be encountered in. cotton plantings (Gossypimn hirsutum) in the state of São Paulo: (a) common yellow mosaic due to the Abutilon mosaic virus; (b) vein mosaic due to an unidentified virus; (c) green mosaic induced by the Brazilian tobacco streak virus and (d) cotton anthocyanosis due to o persistent virus transmitted by the cotton or melon aphid, Aphis gossypii. Cotton yellow mosaic occurs in all plantings, but the percentage of infected plants is usually low; vein mosaic is of rare occurrence; percentage of infection with green mosaic can be high late in the season. The theree types of mosaic are of minor importance under most conditions, no control measure being necessary. Cotton anthocyanosis is at present the most important virus disease of this plant in São Paulo. Late in the season practically all plants become infected. Seed treatment with systemic insecticides and field spraying after the effect of the seed treatment wears off are recommended to reduce aphid infestation and therefore minimize secondary spread of the disease.