Previous data attempting to quantitate the national burden of glomerulonephritis (GN) have been derived from regional biopsy series or end-stage renal disease registries. Wetmore et al. is the first to address this question based on claims data extracted from 2 large U.S. health care systems. Although there are limitations, it provides broad-based epidemiological data that demonstrate a significant underestimate of the extent of GN disease and provide an important first step in its quantitation.