Infection with TT virus (Torque teno virus, TTV), a small, nonenveloped virus with a circular, single-stranded DNA genome classified in the floating genus Anellovirus, is not restricted to humans. Using highly conserved primers derived from the untranslated region of the human TTV genome, a variety of TTV-like viruses have been found circulating in nonhuman primates such as chimpanzees, macaques, and tamarins. TTV variants in nonhuman primates are species-specific, although some genetic groups of human and chimpanzee TTVs cluster to make human/chimpanzee clades. TTVs from macaques and tamarins are increasingly divergent from TTV variants infecting humans and chimpanzees. TTV-like mini virus (TTMV) infections have also been detected in chimpanzees, with genotypes distinct but interspersed with human TTMV genotypes. Pets are also naturally infected with species-specific TTVs, and several isolates have been found in cats and dogs. In addition, other mammals such as tupaias and pigs have species-specific TTVs: swine TTVs are found among pigs worldwide. The genomic organization and proposed transcriptional profiles of TTVs infecting nonhuman primate and other mammalian species are similar to those of human TTVs, and co-evolution of TTVs with their hosts has been suggested. To date, TTVs infecting nonhuman primates and other mammalian species have been under-examined. It is likely that essentially all animals are naturally infected with species-specific TTVs.