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In this study, the cause of rapidly deteriorating renal functions in a follow-up period of a 65-year-old female patient, who applied with nephrotic syndrome findings and diagnosed as membranous nephropathy, is presented. A 65-year-old patient with findings of nephrotic syndromes had normal sizes of kidneys, normal serum complement level, and negative autoantibodies and viral serology. In histopathologic examination, 20 glomeruli was consistent with membranous glomerulonephritis. The patient evaluated as idiopathic membranous nephropathy was montly followed-up with supportive treatment. In the second month of follow-up, re-evaluation of the patient due to nausea and urine discoloration revealed 144 mg/dL urea, 6.3 mg/dL creatinin, 2.5 g/dl albumin. Urine sediment revealed dismorphic erytrocytes and granular silenders. Renal rebiopsy was done. Of 11 glomeruli, 3 global sclerosis, 8 cresentic glomeruli with fibrosis and scarce cellular component were seen. The case was accepted as cresentic glomerulonephritis, a rare complication of idiopathic MN. Before the treatment, anti-GBM, pANCA, cANCA, ANA were negative. Pulse metil prednizolon and pulse endoksan treatment protocol was administered. Hemodialysis was needed 9 times. At the end of the first month of the treatment, hemodialysis was no longer needed. Due to chance of spontaneous remission up to 30% of membranous nephropathy, there is no consensus on specific treatment applicable to all cases. However, cresentic GN should be investigated immediately when sudden and rapid deterioration of renal functions appeared.