Patients with fibrillary glomerulonephritis usually present with nephrotic proteinuria, microscopic hematuria, Impaired renal function, and hypertension; 50% develop end-stage renal disease within a few years. There Is no known effective therapy for fibrillary glomerulonephritis. We describe three patients with biopsy-proven fibrillary glomerulonephritis, in whom pathognomonic fibrillar deposits of 20-nm diameter were seen by electron microscopy. All patients had nephrotic syndrome and normal renal function at the time of diagnosis. They were treated Initially with prednisone, 1 mg/kg body weight, then tapered individually according to the clinical course. Additional therapy consisted of an angiotensin-converting enzyme inhibitor and diuretics. Proteinuria disappeared in two of three patients after 9 and 12 months of therapy. In one patient, proteinuria was reduced from 7.49 mg/mg creatinine to 0.63 mg/mg creatinine after 6 months of treatment. The kidney function remained normal In all three cases. Two patients are now free of steroid therapy for 9 and 6 months. They show no signs of recurrence of kidney disease and have normal renal function without significant proteinuria. Steroid therapy In patients with biopsy-proven fibrillary glomerulonephritis, starting with prednisone, 1 mg/kg body weight, and tapered Individually according to the clinical course, Is a promising strategy. Early start of treatment In patients with preserved renal function seems to be crucial for a favorable outcome. (C) 2002 by the National Kidney Foundation, Inc.