Background <p>This study aimed to assess the link between inflammatory biomarkers (like the neutrophil-to-lymphocyte ratio (NLR), systemic immune-inflammatory index (SII), and systemic inflammation response index (SIRI)) and gallstones in American individuals aged under 50 years.</p> Methods <p>This study utilized data from the National Health and Nutrition Examination Survey (NHANES) covering 2017 to 2020, centering on individuals under 50 years with comprehensive data on NLR, SII, SIRI, and gallstones. It employed a weighted multiple logistic regression approach to investigate the link between inflammatory biomarkers and gallstones. Furthermore, dose-response relationships and threshold effects were evaluated utilizing restricted cubic spline (RCS) methods and segmented linear regression models. Subgroup examinations and interaction assessments were conducted, too.</p> Results <p>The investigation encompassed a total of 3,295 individuals. Upon comprehensive adjustment for variables, multivariate logistic regression revealed a positive relationship between inflammatory biomarkers and gallstones: ln-NLR (OR = 1.68, 95% CI: 1.06–2.66, <i>p</i> = 0.033), ln-SII (OR = 1.79, 95% CI: 1.08–2.98, <i>p</i> = 0.032), and ln-SIRI (OR = 1.46, 95% CI: 1.07–1.99, <i>p</i> = 0.025). A non-linear association, shaped like an inverse “U”, was noted between ln-SIRI and gallstones. To the left of the inflection point (ln-SIRI = 0.35, SIRI = 1.42), a positive link existed between ln-SIRI and gallstones (OR = 2.45, 95% CI: 1.20–5.03); whereas, to the right of the inflection point, the association was statistically insignificant (OR = 0.60, 95% CI: 0.21–1.73).</p> Conclusion <p>ln-NLR and ln-SII exhibited a linear and positive relationship with the likelihood of developing gallstones. ln-SIRI demonstrated a nonlinear dose-response relationship with gallstone risk, characterized by an inverted “U” shape.</p>