Eighteen patients with lupus membranous nephritis were retrospective identified by reviewing the renal biopsy records of an active renal pathology service. Seven had minimally proliferative membranous nephropathy (World Health Organization (WHO) classes Va and b). Eleven had membranous nephropathy with superimposed changes of focal or diffuse proliferative glomerulonephritis (WHO Vc and d). After mean follow-up periods of 73 +/- 6 and 74 +/- 15 mo, respectively, one patient of seven from WHO Va and b and seven of 11 from WHO Vc and d reached end stage renal disease. The latter patients were distinguishable from the former only by the degree of superimposed proliferation on renal biopsy and not by blood pressure, antinuclear antibody, anti-double stranded DNA, or complement levels. These data stand in contrast to the widely held belief that lupus membranous nephropathy is relatively benign. The belatedness of this observation is partially due to imprecision in nosology for patients with lupus who have renal biopsies with "overlap" characteristics.