OBJECTIVE: To clarify the frequency and characteristics of discrepant outcomes of intravenous immunoglobulin (IVIG) between fever and coronary artery aneurysms (CAAs) in patients with Kawasaki disease. STUDY DESIGN: This study included 325 patients who responded to oral aspirin and IVIG alone. The main outcome was CAA 4 weeks after disease onset. CAA was defined as ≥2.5 of maximum z score (Zmax) representing the highest value of 4 coronary artery branches. Immunoglobulin dosage and sequential changes in Zmax were reviewed to investigate the effects on fever and timing of CAA development. Logistic regression analyses with receiver operating characteristic curves using clinical and laboratory variables including the initial Zmax were performed to identify predictors of CAA at 4 weeks. RESULTS: CAAs were either persistent or appeared de novo 4 weeks after diagnosis in 13 of 325 patients who responded to a single or repeated IVIG. Four single-dose IVIG-responders developed CAA although they had pretreatment Zmax of <2.0. The 2 single-dose IVIG responders with the greatest pretreatment Zmax (>4.5) developed persistent CAA. Receiver operating characteristic analysis demonstrated Zmax of 2.57 as the cut-off for predicting CAA. Multivariable analyses identified >2.5 Zmax (OR 9.08, 95% CI 1.26-65.3, P = .028, 50% sensitivity, 91% specificity) as the sole risk factor for CAA at 4 weeks in single-dose IVIG responders. CONCLUSIONS: Delayed development and persistence of CAA in single-dose IVIG responders indicate that some factors other than those responsible for systemic inflammation may contribute to vasculitis in CAA. Baseline Zmax 2.5 aids in predicting CAAs.