BACKGROUND: This study evaluates periodontal conditions and microbiologic findings and their influence on rheumatologic disease parameters in patients with rheumatoid arthritis (RA). METHODS: One hundred and sixty-eight patients with RA were included. A healthy control group (HC, n = 168) was composed according to age, sex, and smoking habits. Rheumatologic data (duration of illness, Disease Activity Score 28, rheumatic factor [RF], anti-cyclic citrullinated peptide [aCCP], medications) were extracted from patients' records. Dental examination included: 1) dental findings (decayed, missing, and/or filled adult teeth [DMF-T] index); 2) gingival inflammation (papillary bleeding index [PBI]); and 3) periodontal status (probing depth [PD], attachment loss [AL]). Periodontal condition was classified as healthy/mild, moderate, or severe periodontitis. Subgingival biofilm was analyzed regarding 11 periodontopathogenic bacteria. Statistical analyses included: 1) Kolmogorov-Smirnov test; 2) Mann-Whitney U test; 3) Pearson χ2 test; 4) Kruskal-Wallis test; and 5) regression analysis; level of significance α = 5%. RESULTS: Mean DMF-T was significantly higher in patients with RA (19.3 ± 4.8) than in HC group (16.9 ± 5.8), especially owing to number of missing teeth (RA = 6.0 ± 5.4, HC = 3.1 ± 3.3; P <0.01). Patients with RA had a significantly higher proportion of increased PD (P <0.01) and AL compared with HC group (P <0.01). Moderate to severe periodontitis was noted in 98% of patients with RA and 82% of the HC group (P <0.01). RF-positive patients with RA suffered from worse periodontal conditions than RF-negative patients (P = 0.01). Age, PBI, and presence of Treponema denticola (P <0.03) are related to periodontal condition in patients with RA. Although not statistically significant, Porphyromonas gingivalis and Fusobacterium nucleatum occur in higher concentrations more often in aCCP-positive patients with RA (P = 0.06). CONCLUSIONS: Patients with RA had worse periodontal conditions than HC participants. Although a trend for higher F. nucleatum and P. gingivalis concentrations in aCCP-positive patients with RA was found, importance of periodontal pathogenic bacteria and rheumatoid parameters in the interrelationship between periodontitis and RA remains unclear.