OBJECTIVE Primary angiitis of the central nervous system (PACNS) is a severe and ill-defined neurologic disease. The goal of this study was to characterize the presenting features, treatment, and neurologic outcome of PACNS in children (cPACNS) and to define the predictors of disease progression in order to identify high-risk patients with cPACNS. METHODS The cohort comprised consecutive patients diagnosed as having cPACNS based on clinical and vascular imaging findings, including identification of arterial stenosis on conventional angiography or magnetic resonance (MR) angiography. Disease progression was defined angiographically at >3 months after initial angiography. Clinical data obtained in prospectively collected standardized assessments and results of laboratory tests, including detection of cerebrospinal fluid abnormalities, were noted, and neuroimaging studies were reanalyzed. Predictors of progression were identified and tested in multivariate regression models. RESULTS Sixty-two consecutive patients with cPACNS (38 male, 24 female, median age 7.2 years) were included. Two distinct subgroups were identified, those with progressive disease and those with nonprogressive disease. Progressive cPACNS was found in 20 of 62 children and was predicted by a clinical presentation of neurocognitive dysfunction, multifocal parenchymal lesions on MR imaging, and evidence of distal stenoses on angiography. CONCLUSIONS The spectrum of PACNS in children includes both progressive and nonprogressive forms. Characteristic features at diagnosis can be used to predict later progression, to identify a distinct high-risk cPACNS cohort, and to help guide selection of patients for immunosuppressive therapy.