BACKGROUND: The patterns and clinical significance of the presence of collaterals in moyamoya disease has not been elucidated thoroughly. We aimed to summarize the clinical features of collaterals in pediatric moyamoya disease. BASIC PROCEDURES: We reviewed consecutive pediatric patients with moyamoya vasculopathy who were admitted to our hospital from 2009 to 2015. Only pediatric moyamoya patients with digital subtraction angiography examinations were included in this study. We classified spontaneous collaterals into two groups by their origins, the internal carotid artery and vertebral artery (ICA-VA)-originated collaterals and the external carotid artery (ECA)-originated collaterals. MAIN FINDINGS: A total of 140 pediatric patients with moyamoya disease (mean age, 10.1 +/- 3.7 years) were included in this study. We identified collaterals originated from ICA-VA in 122 (87.1%) pediatric patients (222 hemispheres). Patients in the ICA-VA collaterals group had similar Suzuki stages with patients without collaterals originated from ICA-VA (mean, 3.86 vs 3.50; P= 0.157). We identified collaterals originated from ECAs in 70 (50.0%) pediatric patients (106 hemispheres) with moyamoya disease. The infarctions were more common in patients with ECA-originated collaterals than in patients without ECA-originated collaterals (25 versus 12; P= 0.021). PRINCIPAL CONCLUSIONS: Our results demonstrate that collaterals originating from ECAs are associated with advanced Suzuki stages and infarction presentations in children with moyamoya disease.