The complete nucleotide sequences of two isolates of Pennisetum mosaic virus (PenMV) were determined. The viral genome comprised 9,611 nucleotides (nt) excluding the 3'-terminal poly(A) sequence, with the capacity of encoding a single polyprotein of 3,065 amino acids. The large open reading frame is flanked by a 172-nt 5'-untranslated region (UTR) and a 244-nt 3'-UTR. Sequence comparisons and phylogenetic analyses of the complete genome and polyproteins suggest that PenMV is closely related to other monocot potyviruses such as Maize dwarf mosaic virus, Sorghum mosaic virus and Sugarcane mosaic virus (SCMV), and thus represents a distinct potyvirus within the SCMV subgroup. The host range of PenMV is limited to Gramineae, and the virus naturally infects maize, sorghum and some wild grasses, causing mosaic symptoms on the leaves. This virus could be transmitted by both mechanical inoculation and by at least four species of aphids.