Membranous nephropathy (MN) is a frequent cause of nephrotic syndrome in adults. A considerable diversity of prognosis is seen with idiopathic MN. We overview the recent progress of clinicopathological research, especially the initial factors affecting the longterm outcome of idiopathic MN. We studied retrospectively 105 patients with idiopathic MN and could assign the patients to two different groups based on the electron microscopic (EM) findings. In the homogeneous type only one patient developed end-stage renal failure, and earlier remission occurred in this group. With regard to secondary outcome, increased age, focal segmental glomerular sclerosis, arteriolosclerosis, heterogeneous type of EM findings were independent risk factors. Our results suggest that a new EM classification at initial biopsy is an independent indicator of prognosis in human idiopathic MN.