Background : Hunting and butchering of wild non-human primates infected with simian immunodeficiency virus (SIV) is thought to have sparked the HIV pandemic. Although SIV and other primate retroviruses infect laboratory workers and zoo workers, zoonotic retrovirus transmission has not been documented in natural settings. We investigated zoonotic infection in individuals living in central Africa. Methods : We obtained behavioural data, plasma samples, and peripheral blood lymphocytes from individuals living in rural villages in Cameroon. We did serological testing, PCR, and sequence analysis to obtain evidence of retrovirus infection. Findings : Zoonotic infections with simian foamy virus (SFV), a retrovirus endemic in most Old World primates, were identified in people living in central African forests who reported direct contact with blood and body fluids of wild non-human primates. Ten (1%) of 1099 individuals had antibodies to SFV. Sequence analysis from these individuals revealed three geographically-independent human SFV infections, each of which was acquired from a distinct non-human primate lineage: De Brazza's guenon (Cercopithecus neglectus), mandrill (Mandrillus sphinx), and gorilla (Gorilla gorilla), two of which (De Brazza's guenon and mandrill) are naturally infected with SIV. Interpretation : Our findings show that retroviruses are actively crossing into human populations, and demonstrate that people in central Africa are currently infected with SFV. Contact with non-human primates, such as happens during hunting and butchering, can play a part in the emergence of human retroviruses and the reduction of primate bushmeat hunting has the potential to decrease the frequency of disease emergence.