Approximately 15-20% of patients with Kawasaki disease (KD) are not responsive to high-dose intravenous gammaglobulin (IVIG). We have previously reported a predictive method for identifying IVIG-non-responsive patients (high-risk KD patients). We determined the safety and effectiveness of pulse methylprednisolone with high-dose IVIG (mPSL+IVIG) as a primary treatment for high-risk KD patients. Sixty-two high-risk KD patients were treated with pulse methylprednisolone 30 mg/kg over 2 h, followed by IVIG 2 g/kg over 24 h (mPSL+IVIG group) and were compared with a historical control group of 32 high-risk patients treated with IVIG 2 g/kg alone at the participating hospitals before this study was opened (IVIG group). High-risk patients were identified with at least two of three predictors (C-reactive protein >or=7 mg/dL, total bilirubin >or=0.9 mg/dL or aspartate aminotransferase >or=200 IU/L). Sixty-six percent (95% confidence interval [CI] 54-78%) of patients had a prompt defervescence in the mPSL+IVIG group compared with 44% (95% CI 26-62%) for the IVIG group (p=0.048). Coronary artery lesions were observed in 24.2% (95% CI 13.2-35.2%) and 46.9% (95% CI 28.6-65.2%) of patients in the mPSL+IVIG and IVIG groups, respectively (p=0.025). This is the first report showing that mPSL+IVIG is effective and safe as a primary treatment for high-risk KD patients.