The data were presented in abstract form at the 45th meeting of the American Society of Nephrology, October 30-November 04 2012, San Diego, CA, USA. Circulating autoantibodies against M-type phospholipase A2 receptor (PLA2R) are important pathogenic antibodies of idiopathic membranous nephropathy (MN) in adults. However, previous studies on the clinical impact of anti-PLA2R antibodies demonstrated several limitations, including insufficient numbers of study subjects and different time points and methods for anti-PLA2R antibody measurement. To verify the clinical significance of anti-PLA2R antibodies in Korean patients with MN, we measured autoantibodies in serum samples obtained at the time of biopsy from a total of 100 patients with idiopathic MN who had not yet received immunosuppressive treatment. We detected anti-PLA2R antibody in 69 patients, and we observed that autoantibody reactivity reflected the severity of disease activity. Proteinuria and hypoalbuminemia were more severe in patients with anti-PLA2R than in those without the autoantibodies (2.95 g/g vs. 6.85 g/g, P = 0.003; 3.1 g/dL vs. 2.5 g/dL, P = 0.004, respectively). Additionally, the clinical severities worsened proportionally as the levels of anti-PLA2R antibodies increased (P = 0.015 and P for trend <0.001 for proteinuria and hypoalbuminemia, respectively). However, neither the levels nor the presence or absence of anti-PLA2R antibody showed a significant correlation with clinical outcomes, such as remission rate and time to remission. In conclusion, we observed that anti-PLA2R antibodies are highly prevalent in Korean patients with idiopathic MN and that they reflect the clinical disease activity before the administration of immunosuppressive treatment. However, the levels of anti-PLA2R antibody at the time of kidney biopsy may not predict the clinical outcomes in current clinical practice.