We describe 2 patients with mantle cell lymphoma who presented with dialysis-dependent acute renal failure and in whom the renal biopsies showed proliferative glomerulonephritis. The first patient had lymphadenopathy and the second splenomegaly, but no cause was initially identified in either case. The first patient was treated with immunosuppressive drugs, the second was given no specific therapy; renal function recovered in both. However, more than 1 year later, both again became dialysis-dependent but had also developed generalized lymphadenopathy. A diagnosis of mantle cell non-Hodgkin's lymphoma was made in both cases. The association of active lymphoma and renal disease supports a paraneoplastic mechanism for the occurrence of the glomerulonephritis in these patients. The literature describing the association between non-Hodgkin's lymphoma and glomerulonephritis is reviewed.