In this issue of AJKD, Caravaca-Fontán et al1 describe a large series of cases of C3 glomerulopathy (C3G), one of the most rare and complex types of glomerular disease. The authors focus on factors impacting outcome and validate a chronicity scoring system as an independent prediction factor. Although C3G is rare, with an estimated prevalence of 5 cases per 1,000,000,2 this disorder is one of the most interesting. The rapidly evolving scientific understanding of its basic mechanism has pinpointed dysregulation of the complement system as the key pathophysiologic event.