BACKGROUND: Inflammatory bowel disease (IBD), including Crohn's disease (CD) and ulcerative colitis (UC), poses a significant challenge to health care systems because of its chronic nature and increasing global prevalence. Effective management of IBD requires accurate diagnostic tools and biomarkers. This systematic review and meta-analysis aimed to evaluate the relationship between bilirubin concentrations and IBD activity and outcomes. METHODS: A comprehensive search of electronic databases identified 11 studies that included 2606 subjects with IBD and 3607 healthy controls. RESULTS: Bilirubin concentrations were significantly lower in subjects with IBD when compared to controls (SMD = -0.96, 95% CI -1.21 to -0.70; p < .001). Although substantial heterogeneity was observed, sensitivity analysis confirmed the robustness of the results. Publication bias was detected, but subgroup analyses did not significantly alter the results. Meta-regression showed that age was a significant factor influencing the association between bilirubin concentrations and IBD. Subgroup analyses showed a more pronounced reduction in bilirubin concentrations in subjects with CD than those with UC. CONCLUSION: This study supports the potential utility of bilirubin as a biomarker in IBD, emphasizing the need for further research to validate its clinical significance.