Before an empiric malaria treatment program, >60% of Liberian refugees had malaria on arrival to Minnesota. We compared microscopy with rapid antigen testing for detecting asymptomatic parasitemia. Nine of 103 (8.7%) had malaria by polymerase chain reaction (blood smear and rapid testing had a sensitivity of 22%). The empiric treatment program has decreased the rate of imported asymptomatic malaria. Blood film and rapid antigen testing are poor screening tests.