Introduction: The interferon regulatory factor 5 (IRF5) gene is implicated in the toll‑like receptor signaling pathway and has proinflammatory and chemotactic effects, but its role in the pathogenesis of rheumatoid arthritis (RA) remains unclear. Since the pathobiology of RA shares some similarities with other autoimmune diseases, we tested the hypothesis that RA may be associated with IRF5‑related pathways, as has been reported for systemic lupus erythematosus and Sjögren syndrome. Objectives: The aim of the study was to investigate the association between the presence of methylation in the IRF5 promoter and the morbidity and severity of RA as well as with levels of inflammatory markers. Patients and methods: A total of 146 unrelated individuals, 122 patients with RA and 24 healthy controls, were enrolled in the study. All RA patients were genotyped with regard to the following polymorphisms in the IRF5 gene: rs10488631, T>C and rs4728142 G>A. The methylation analysis included 52 patients with RA and 24 healthy controls. A quantitative real‑time methylation‑specific polymerase chain reaction was used to evaluate methylation status. Results: We found differences between patients with RA and healthy controls in the methylation pattern of the promoter region. The methylation level was 43.6% lower in RA patients than in controls (median [interquartile range], 0.79 [0.6-1.13] vs 1.4 [1.16-1.66]; P = 0.0001). Variant rs4728142 G>A was more common in seronegative patients with RA. Conclusions: The methylation profile of the IRF5 promoter may be used as a new potential marker of RA, which is independent of current criteria of disease activity.