Renal lesions in ANCA-associated vasculitis (AAV) show an absence or paucity of immune deposits. Therefore, complement was not considered a major pathogenic factor. Data from an animal model of AAV, however, suggest involvement of the alternative pathway of complement. The paper by Gou et al. demonstrates activation also of the alternative and final common pathways in patients with AAV. Thus, the complement system might be a target for treatment in human AAV.