Background <p>High mobility group box protein 1 (HMGB1) exhibits pro-inflammatory functions in chronic inflammatory diseases and is closely associated with other inflammatory markers contributing to sustained inflammatory milieu. This study aimed to evaluate HMGB1 levels and their associations with tumor necrosis factor alpha (TNFα), transforming growth factor beta (TGFβ) and interleukin- 1b (IL-1β) in the saliva and serum of the periodontitis patients.</p> Methods <p>Sixty-six systematically healthy nonsmoker individuals were enrolled and categorized into three groups: (1) Control, (2) Stage I-II Periodontitis, and (3) Stage III-IV Periodontitis. Comprehensive periodontal assessments were performed. HMGB1, TNFα, IL-1β and TGFβ concentrations were analyzed by enzyme-linked immunosorbent assay (ELISA). One-way ANOVA with Tukey’s post-hoc test assessed group differences, and Pearson’s correlation evaluated relationships between quantitative variables.</p> Results <p>Salivary HMGB1 levels were significantly elevated in both periodontitis groups compared to controls (<i>p</i> &lt; 0.0001). Serum HMGB1 levels were significantly higher in the Stage III–IV periodontitis group than in both the control (<i>p</i> = 0.022) and Stage I–II (<i>p</i> &lt; 0.001) periodontitis groups. Serum HMGB1 showed positive correlations with IL-1β levels in both periodontitis groups (<i>p</i> &lt; 0.05 for Stage I–II; <i>p</i> ≤ 0.01 for Stage III–IV). A significant positive correlation was also observed between salivary HMGB1 and TNFα levels in the Stage I–II periodontitis group (<i>p</i> ≤ 0.01).</p> Conclusion <p>HMGB1 levels increase in saliva and serum as periodontal disease worsens, suggesting enhanced HMGB1 expression was involved in the pathogenetic shifts in the disease process at local and systemic levels.</p>