Simian adenovirus 1 (SAdV-1) is one of many adenovirus strains that were isolated from Old World monkey cells during poliomyelitis vaccine production several decades ago. Despite the availability of these viruses, knowledge of their genetic content and phylogeny is rudimentary. In the present study, the genome sequence of SAdV-1 (34,450 bp) was determined and analysed. In regions where genetic content varies between primate adenoviruses, SAdV-1 has a single virus-associated RNA gene, six genes in each of the E3 and E4 regions and two fiber genes. SAdV-1 clusters phylogenetically with HAdV-40, a member of human adenovirus species HAdV-F, which also has two fiber genes. However, based on phylogenetic distances and other taxonomic criteria, SAdV-1 is proposed to represent a novel adenovirus species.