['Modification of antigens represents a trigger for the generation of autoantibodies. In the pathogenesis of rheumatoid arthritis (RA), citrullination of proteins has been shown to be a critical process, and the determination of antibodies against citrullinated antigens has been a diagnostic milestone. We undertook this study to determine whether antibodies to mutated and citrullinated vimentin (MCV) could serve as a diagnostic and prognostic marker for RA.', 'We identified novel isoforms of human MCV in the synovial fluid of RA patients. The significance of these disease-related modifications was investigated by the analysis of autoantibody reactivities. In a group of 1,151 RA patients, the diagnostic significance and the prognostic value of an anti-MCV enzyme-linked immunosorbent assay (ELISA) were compared with that of an anti-cyclic citrullinated peptide (anti-CCP) ELISA.', 'In RA, sensitivities of 82% and 72% were calculated for the anti-MCV and anti-CCP assays, respectively. The specificity of both assays was comparable (98% and 96%, respectively). In followup analyses of 16 RA patients with moderate disease activity (mean Disease Activity Score in 28 joints [DAS28] of 2.72) and 26 RA patients with active disease (mean DAS28 of 5.07), disease stratification of RA was possible using the anti-MCV assay (P = 0.0084). A significant correlation of anti-MCV antibodies with the DAS28 was documented (r = 0.5334, P = 0.0003), in 42 RA patients (n = 427 antibody determinations at different time points).'] Does mutation and citrullination modify vimentin to a novel autoantigen for rheumatoid arthritis?