Yellow dwarf disease, one of the most important diseases of cereal crops worldwide, is caused by virus species belonging to the Luteoviridae family. Forty-two virus isolates obtained from oat (Avena sativa L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), corn (Zea mays L.), and ryegrass (Lolium multiflorum Lam.) collected between 2007 and 2008 from winter cereal crop regions in southern Brazil were screened by polymerase chain reaction (PCR) with primers designed on ORF 3 (coat protein - CP) for the presence of Barley yellow dwarf virus and Cereal yellow dwarf virus (B/CYDV). PCR products of expected size (~357 bp) for subgroup II and (~831 bp) for subgroup I were obtained for three and 39 samples, respectively. These products were cloned and sequenced. The subgroup II 3' partial CP amino acid deduced sequences were identified as BYDV-RMV (92 - 93 % of identity with "Illinois" Z14123 isolate). The complete CP amino acid deduced sequences of subgroup I isolates were confirmed as BYDV-PAV (94 - 99 % of identity) and established a very homogeneous group (identity higher than 99 %). These results support the prevalence of BYDV-PAV in southern Brazil as previously diagnosed by Enzyme-Linked Immunosorbent Assay (ELISA) and suggest that this population is very homogeneous. To our knowledge, this is the first report of BYDV-RMV in Brazil and the first genetic diversity study on B/CYDV in South America.