Raspberry bushy dwarf idaeovirus (RBDV) has an unusual combination of properties and has been classified as the sole member of a new plant virus genus, for which the name idaeovirus has been proposed. Particles of RBDV resemble those of ilarviruses (family Bromoviridae) in appearance and in being transmitted in association with pollen. RBDV has 2 genomic RNA species, RNA-1 (5449 nt) and RNA-2 (2231 nt). The particles also contain RNA-3 (946 nt), a subgenomic monocistronic coat protein mRNA which is derived from the 3′ end of the bicistronic RNA-2. The single 190 K protein encoded by RNA-1 contains methyltransferase, helicase and polymerase domains. Evolutionary distance data obtained from multiple alignments of the amino acid sequence of the RBDV 190 K protein and corresponding proteins with replicative function from other plant viruses suggest that the closest affinities of RBDV are with the tripartite genomed viruses in the family Bromoviridae. It is proposed that the genus idaeovirus be included in the family Bromoviridae.