Hirano D, et al. - In this retrospective Japanese multicenter study, researchers analyzed the clinical characteristics as well as outcomes of childhood-onset anti-neutrophil cytoplasmic antibody (ANCA)–associated vasculitis (AAV), especially microscopic polyangiitis (MPA). This study included 49 patients with AAV, 36 being female. MPA (n = 38, 78%), granulomatosis with polyangiitis (n = 9, 18%), eosinophilic granulomatosis with polyangiitis (n = 1, 2%), and other (n = 1, 2%) were the diagnoses. The estimated prevalence of 3.41–4.28 per million children was reported for childhood-onset AAV. Predominantly, females were affected by childhood-onset AAV. The disease was characterized by a high frequency of detection in school urinary screening programs. Progression to end-stage renal disease (ESRD) without achieving remission was still reported in more than 10% of patients with childhood-onset AAV. With ESRD, a relation of histological chronicity was evident.