Background: Central nervous system inflammation sometimes occurs in Kawasaki disease (KD). In 2012, we reported the first case of KD complicated with mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) in a 14-year-old. Since then, similar cases have been reported. We studied the incidence of KD complicated with encephalitis/encephalopathy and MERS. Methods: We selected 36 patients (22 boys and 14 girls; age: range, 5-80 months; mean, 22 months) from 42 patients who had undergone electroencephalography (EEG) before intravenous immunoglobulin (IVIG) therapy between May 2013 and August 2014. Patients with and without abnormal EEG findings were assigned to groups A and B, respectively. Age; sex; time of diagnosis; neurological symptoms; N-terminal pro-brain natriuretic peptide, serum procalcitonin, serum sodium, serum albumin, and C-reactive protein (CRP) levels; liver disorder, coronary artery lesion, and IVIG therapy response were examined. Results: Group A comprised 6 patients (17%); and group B, 30 patients (83%). Consciousness disturbance was noted in 5 of 6 patients with abnormal EEG findings, without sequelae. Patients in group A were significantly older (56.5±16.8 vs 25.0±19.9 months ) and had higher CRP levels than those in group B (12.3±5.62 vs 6.56±3.47 mg/dL ). No other parameters showed significant differences. Magnetic resonance imaging revealed edema in 2 of 5 patients and MERS in the remaining patient in group A. Pleocytosis was noted in 1 of 4 patients in group A. Cytokine Il-6 and INF-γ levels were very high in the patient with MERS. Conclusion: EEG findings indicating central nerve disorders were noted in 17% patients, a lower incidence than that reported by Mitudome et al . We performed EEG early before IVIG therapy; thus, central nerve symptoms encountered may have occurred in the early stages of the disorders. MERS was noted in 1 of 6 patients with abnormal EEG findings, or 2 of 9 patients if past cases with neurological symptoms were included, suggesting that central nerve complications occur in a certain group of KD patients.