Resistance of Plasmodium species to antimalarial agents has become increasingly challenging to the management and prevention of malaria. We experienced an imported case of tertian malaria due to Plasmodium vivax relapsed after a seemingly successful treatment with conventional course of hydroxychloroquine and primaquine. A 35-year-old man developed fever three days after return from India and mainland China. After his illness was diagnosed as tertian malaria, he was managed with hydroxychloroquine and then primaquine (primaquine base 15 mg/day for 14 days). Thereafter peripheral blood smears showed no malarial parasites, and there was no relapse of symptom until the 55th post-treatment day, however, six months after the above treatment tertian malaria relapsed. He was managed with the same medications again and malaria did not relapse for 10 months.
