Postinfectious glomerulonephritis that fails to resolve following resolution of the underlying infection or that develops in the absence of any evidence of a preceding infection has been termed atypical postinfectious glomerulonephritis. Activation of the alternative pathway of complement occurs in patients who develop postinfectious glomerulonephritis. Sethi et al. have now shown that among 11 patients with atypical glomerulonephritis (six of whom had no evidence of preceding infection), 10 had underlying abnormalities in the alternative pathway of complement, suggesting a possible mechanism by which this disease occurs.