Copyright © 2017 by The American Association of Immunologists, Inc. Autoimmunity has been implicated in the pathogenesis of idiopathic pulmonary fibrosis (IPF); however, the repertoire of autoantigens involved in this disease and the clinical relevance of these autoimmune responses are still being explored. Our initial discovery assays demonstrated that circulating and intrapulmonary vimentin levels are increased in IPF patients. Subsequent studies showed native vimentin induced HLA-DR-dependent in vitro proliferation of CD4 T cells from IPF patients and enhanced the production of IL-4, IL-17, and TGF-b1 by these lymphocytes in contrast to normal control specimens. Vimentin supplementation of IPF PBMC cultures also resulted in HLA-DR-dependent production of IgG with anti-vimentin specificities. Circulating anti-vimentin IgG autoantibody levels were much greater in IPF subjects from the University of Alabama at Birmingham (n = 102) and the University of Pittsburgh (U. Pitt., n = 70) than in normal controls. Anti-vimentin autoantibody levels in IPF patients were HLA biased and inversely correlated with physiological measurements of lung function (i.e., forced expiratory volumes and diffusing capacities). Despite considerable intergroup differences in transplant-free survival between these two independent IPF cohorts, serious adverse outcomes were most frequent among the patients within each population that had the highest anti-vimentin autoantibody levels (University of Alabama at Birmingham: hazard ratio 2.5, 95% confidence interval 1.2-5.3, p = 0.012; University of Pittsburgh: hazard ratio 2.7, 95% confidence interval 1.3-5.5, p = 0.006). These data show that anti-vimentin autoreactivity is prevalent in IPF patients and is strongly associated with disease manifestations. These findings have implications with regard to the pathogenesis of this enigmatic disease and raise the possibility that therapies specifically directed at these autoimmune processes could have therapeutic efficacy.