Fibrillary glomerulonephritis (FGN) is a rarely diagnosed disease with clinical manifestations such as proteinuria, microscopic hematuria, nephrotic syndrome or decreased kidney function. Around one half of patients develop chronic renal failure in the course of several years. The diagnosis of fibrillary glomerulonephritis is to be established only basing on the results of renal biopsy. Pathognomonic is the electron-microscopic examination, evidencing fibrillar deposits in mesangium and in basal membranes of glomeruli. Fibrils are similar to those seen at amyloidosis, however, with larger diameter, non-linear deposition and do not stain with Congo red or thioflavin T. Immunofluorescency test usually shows the presence of IgG, namely the subclasses IgG4, C3 and
and  of light immunoglobulin chains. The presented case report describes clinical and laboratory findings at a patient suffering from nephrotic syndrome. Results of renal biopsy and detailed histological examinations concluded the diagnosis as fibrillary glomerulonephritis. The patient was treated with a combination of prednisone (1 mg/kg/24 hrs) with cyclophosphamide (2 mg/kg/24 hrs) for six months. This led to a decrease of proteinuria from the initial value of 5.38 g/24 hours to 1.88 g/24 hours, as well as to a partial remission of nephritic syndrome. Glomerular filtration, evaluated using endogenous creatinine clearance, remained within limits of normal values throughout the follow-up, with the value of 2.6 ml/s after the treatment.

        Key words: Nephrotic syndrome - Renal biopsy - Fibrillary glomerulonephritis - Immunotactoid glomerulopathy - Amyloidosis