The genus Synolcus Loew, 1858 is fully revised. This southern African endemic has 13 valid species, of which four are newly described: armstrongi (South Africa: KwaZulu-Natal), macrocercus (South Africa: Western Cape and Northern Cape), namibiensis (southern Namibia), ukhahlamba (South Africa: KwaZulu-Natal). Asilus incisuralis Macquart, 1838 is a new synonym of Asilus acrobaptus Wiedemann, 1828. All species are described or redescribed, illustrated and mapped. A key for their identification is provided, while the taxonomy, distribution and biology of the group are discussed.