The nucleotide sequences of all genome segments of the Nilaparvata lugens reovirus (NLRV), which is found in the brown planthopper Nilaparvata lugens, have been determined and some genes have been assigned to structural and functional proteins. The genome of NLRV consists of 28 699 nucleotides and contains at least 11 large open reading frames (ORFs). The genome of NLRV is the largest among viruses of the family Reoviridae reported to date. The deduced amino acid sequence of genome segment S1 contained the major motifs of RNA polymerase and that of S7 had the purine NTP-binding motif. Based on the molecular masses of the deduced proteins and the particle structure of NLRV, segments S1, S3 and S7 were assigned to the 160, 140 and 75 kDa proteins, respectively, that are located in the inner core. It was deduced that S2 codes for the 135 kDa protein (B spike), which is located on the surface of the inner core. Most reported ORFs of rice black streaked dwarf virus (RBSDV), which shares many properties with NLRV, had similarities with the corresponding ORFs of NLRV. An exception was S7 ORF2, which is found in RBSDV but not NLRV and may therefore be involved in multiplication of RBSDV in rice plants. These results and our previous observations indicate that NLRV should be classified in the genus Fijivirus.