In the glomerulonephritides of systemic lupus erythematosus (SLE), the number of subendothelial deposits, when present, generally corresponds to the degree of light microscopic glomerular hypercellularity; only very rarely are no or few such deposits present in cases of focal (WHO class III) or diffuse (WHO class IV) proliferative lupus nephritis. We have recently encountered five cases of active diffuse proliferative glomerlonephritis with no subendothelial and few or no mesangial deposits and thrombotic microangiopathy (TMA) in four patients with SLE and one patient with lupus-like syndrome. Three of the five patients were tested for circulating lupus anticoagulants or anticardiolipin antibodies, and two were positive. All five patients tested negatively for antineutrophil cytoplasmic antibodies (ANCA). Three patients responded to steroid and cyclophosphamide treatment, although one of them died of acute bacterial bronchopneumonia. One patient was lost to follow-up. We conclude that "pauci-immune" proliferative lupus nephritis is rare and should be treated as proliferative lupus nephritis with a proportionate number of subendothelial deposits. The negative ANCA suggests that these cases do not represent incidental ANCA-associated pauci-immune necrotizing and crescentic glomerulonephritis in patients with SLE. Of particular interest is that, in patients with SLE, if associated with TMA, an active proliferative necrotizing glomerulonephritis may be present even in the absence of significant glomerular immune complex deposition.