We report a case of a 65-year-old man presenting with multicentric Castleman's disease (MCD) accompanied by membranoproliferative glomerulonephritis-like lesion with fibrillary deposits. The lesion was characterized by highly organized ultrastructual deposits that were negative for Congo-red stain and for immunoglobulin, light chain and C3. Thus, this renal lesion was considered histologically to be fibrillary glomerulonephritis presenting by light microscopy as mesangiocapillary glomerulonephritis. To our knowledge, among the limited number of cases of renal lesion associated with MCD ever reported, this is the first case of a biopsy-proven fibrillary glomerulonephritis. Serum interleukin 6 (IL-6), known as an indicator of MCD activity and as an autocrine growth factor for mesangial cells, was chronologically measured. Augmentation of urinary IL-6 simultaneously with that of extra renal symptoms of MCD and associated renal disease may indicate an underlying role of this cytokine in the present case. Failure to detect of IL-6 in the glomeruli may support the notion that IL-6 is derived from extrarenal lymphonodi, and not to an in situ product of the glomeruli. However, it may have been related to glomerular injury.