Neutrophils are the major antimicrobial cells of the innate immune system, which are recruited rapidly to the sites of infection and provide the primary defense against pathogens. Recent evidence suggests that neutrophils undergo a distinct cell death mechanism called NETosis, which not only contributes to the host defense, but also leads to severe pathological immune responses in cases of dysregulation. Here, we review the general features of NETosis as well as the generation of autoantigens and damage-associated molecular patterns by NETosis in autoimmune diseases. This review discusses the pathogenic role of NETosis in rheumatoid arthritis and systemic lupus erythematosus, where neutrophils may play a key role in the pathogenesis of these diseases, and suggest the possibility of neutrophil extracellular traps as biomarkers and therapeutic targets for the treatment of autoimmune diseases. (J Rheum Dis 2016;23:82-87)