We have molecularly cloned and determined the nucleotide sequence of the 3' and 5' regions of the genomic RNA of the paramyxovirus simian virus 5 (SV5), including the 3' leader sequence, nucleocapsid protein (NP) gene, large (L) protein gene, and 5' anti-genomic leader (trailer) sequence. The vRNA 3' proximal leader sequence contains 55 nucleotides. The NP gene is 1725 nucleotides in length and encodes a negatively charged protein consisting of 509 residues (MW 56,534). A comparison of the amino acid sequences of 10 paramyxovirus NP proteins indicates a region of high sequence identity near the middle of the protein, and a C-terminal region which is enriched in negatively charged residues. Overall, the SV5 NP protein showed the highest degree of sequence identity with the NP proteins of parainfluenza type 2 virus (58%) and mumps virus (56%). The L gene extends 6804 nucleotides and encodes a positively charged protein consisting of 2255 residues (MW 255,923). The 5' proximal region of the vRNA consists of a 31 nucleotide trailer RNA. The SV5 L protein sequence showed 62% overall identity with the parainfluenza type 2 L protein. Although little overall sequence identity was found between the SV5 and other paramyxovirus L protein sequences, short stretches of extensive amino acid identity were found near the middle of each of the known paramyxovirus L protein sequences, and these common regions may represent sites important for enzymatic activity.