Mosquito-transmitted diseases represent one of the greatest health risks when traveling to tropical and sub-tropical countries. Only Japanese encephalitis and yellow fever can be avoided by inoculation, and only malaria can be prevented by chemoprophylaxis. Exposure prophylaxis is the only protection against all other mosquito-born diseases. These infections need to be carefully considered in the differential diagnosis of returning travelers, taking current epidemiology into account. This review discusses common infectious diseases and the options for their diagnosis and therapy.