Sabiá virus, one of five arenaviruses from South America known to cause hemorrhagic fever in humans, emerged in 1990 when it was isolated from a fatal case in Sao Paulo, Brazil. Subsequently, it has caused two laboratory-acquired infections. Its natural distribution and host are still unknown. Using viral RNA and multiple polymerase chain reaction products as templates, the nucleotide sequence of the small (S) RNA segment of Sabiá virus, which codes for the nucleocapsid (N) and glycoprotein precursor, was determined. This virus shares an ambisense genome in common with other arenaviruses, although it has a unique predicted three stem--loop structure in the S RNA intergenic region. Phylogenetic analysis of a portion of the N gene sequence confirmed that Sabiá virus is distinct from all other members of the Arenaviridae and shares a progenitor with Junin, Machupo, Tacaribe, and Guanarito viruses.