In rheumatoid arthritis (RA) viral triggers, especially Epstein-Barr virus (EBV) and cytomegalovirus (CMV), have been suggested. By PCR analysis DNA of several viruses among which EBV, CMV, and parvovirus B19 (B19) has been detected in RA synovial fluid and synovial tissue. In 63 synovial tissues of 29 rheumatoid arthritis (RA), 6 psoriatic arthritis (PsA), 26 reactive arthritis/synovitis (rA/S), and two normal synovial cases, we recently could demonstrate a high percentage of replicative B19 infection within the synovial tissue, being significantly more frequent in autoimmune arthritis. To further investigate the influence of synovial virus infections in rheumatoid arthritis, we now analyzed the same sample of synovial tissues for CMV and EBV infections by DNA-in situ hybridization (CMV), EBER1/2-RNA-in situ hybridization (EBV), and immunohistochemistry. A significant latent EBV infection of synovial lining cells, synovial fibroblasts, and/or infiltrating lymphocytes was identified in 5/29 (17.2 %) RA, 1/6 (16.7%) PsA, and to a much lower degree in 1/26 (3.8%) rA/S specimens. CMV-DNA was detected in 31% of RA, 3/6 (50%) of PsA, and 11.5% of rA/S. Immunohistochemical analysis of CMV early antigen revealed replicative CMV activity in 20.7% of RA and 2/6 (33.3%) of PsA specimens but not in reactive arthritis synovia. Comparative analysis of the EBV-, CMV-, and published B19-data demonstrated that relevant synovial virus infections in general and furthermore double or multiple infections are far more common in autoimmune arthritis than in rA/S. A triple virus infection was found solely in RA in 10.3% of cases. The evidence of increased synovial persistence of EBV, CMV, or B19 either alone or even more as coinciding infections may further reinforce the notion of a primary role of these viruses in autoimmune arthritis.