To predict resistance to intravenous immunoglobulin (MIG) treatment in patients with severe Kawasaki disease (KD), Gunma, Kurume, and Osaka risk scores were established. Using these scores, prospective randomised trials were performed, and addition of predni- solone or intravenous methylprednisolone -pulse to the standard regimen of IVIG improves coronary artery outcomes in severe KD. Adding the evidences of new and existing therapies, such as infliximab, cyclosporin A, ulinastatin, and plasma exchange, the clinical guideline for medical treatment of the acute phase of KD was revised in 2012. Additional large cohort studies are needed to clarify the applicability of intensive initial treatment. Challenges for the future are: 1) clarification of etiology and establishment of specific therapy, 2) establishment of personalized therapy using genetic markers related to the severity of KD.