Getah virus (GEV), a member of the Semliki Forest (SF) virus complex of alphaviruses, was first isolated in 1955 from a pool of Culex gelidus collected near Kuala Lumpur, Malaysia by suckling-mouse-brain inoculation. Getah species belongs to the SF complex and consists of four subtypes: GEV, Sagiyama virus, Bebaru virus, and Ross River virus. Many virus strains of GEV consist of virus populations with a wide range of plaque sizes. Strains of GEV are highly variable in nature, and differences in host susceptibility to the variant or mutant may play an important role in determining the composition of a virus strain and the evolution of a new strain. Studies on the mechanisms of variation and of acquiring virulence for the host are very important, not only in GEV but also in other alphaviruses. GEV and Sagiyama virus show different behavior in hemagglutinin production. Consistent clinical signs of infection with GEV are seen only in horses.