The microbiota and dysbiosis are involved in various diseases. Many studies in mice and humans demonstrate its influence on inflammatory rheumatisms. In rheumatoid arthritis (RA), Prevotella copri, a Gram-negative bacteria of the intestinal flora, is found to be more prevalent in the early stages of the disease. Specific antibodies against this germ have been identified in RA patients, suggesting a role of this bacteria in the initiation of the disease. Oral microorganisms involved in periodontitis have also been associated with the development and the activity of RA. These discoveries imply new targets in the management of inflammatory rheumatisms.