The purpose of this study is to determine whether two distinct histopathological-immunopathological lesions, which have been reported in severe lupus nephritis, diffuse global glomerulonephritis (GN) (WHO IV) and a segmental and necrotising GN (WHO III) can be reported to coexist in a single patient. We examine the evidence of coexistence of these disparate lesions and the prognostic significance in a group of patients with severe lupus nephritis who have been subjected to a common therapeutic regimen by protocol. The simple, reproducible parameter indicating the presence of glomerular capillary necrosis was the presence of crescents. We, therefore, reviewed 39 renal biopsies with diffuse global lupus GN (WHO IV) (Churg, J, Sobin, LH. Lupus nephritis. Renal disease, classification and atlas of glomerular diseases. New York: Igaku-Shoin; 1982. p. 127-149). and used crescents as a surrogate for glomerular necrosis. Peripheral capillary immune deposits were less prominent in WHO IV with crescents compared with those without and resembled the reduced immune deposits seen in severe segmental GN (WHO III >or= 50%). Patients with WHO IV with crescents had decreased survival without end-stage renal disease (P = 0.02), fewer remissions (P = 0.04) and more adverse outcomes (12/22 vs 3/17) (P = 0.02) than those without crescents, and this was similar to patients with WHO III >or=50%. We conclude that, on the basis of immunological and morphological features, WHO IV with crescents appears to be the result of two distinct pathogenetic mechanisms. We propose that diffuse global lupus GN, associated with crescents, is best described as WHO class IV + WHO class III.