Hypersensitivity syndrome (HS) has been recognized as one of severe adverse drug eruptions. HS has several characteristic features as follows. First, the clinical symptoms are high fever, multiple lymphadenopathy, severe skin rash, mononucleosis and multiple visceral involvement. Secondly, those symptoms appear two to six weeks after the initiation of drug administration. Thirdly, HS is induced by the specific drugs, carbamazepine, phenytoin, salazosulfapyridine, allopurinol, diaphenylsulphone, and mexiletine. Recently, we reported the association of HS with reactivation of HHV-6, the causative virus for exanthem subitum. We propose the new disease entity of HHV-6-associated drug eruption (HADE) because HS is composed of two clinical phases, drug allergic reaction in the early phase and HHV-6 reactivation in the late phase.