Context.-Bilirubin has strong anti-inflammatory and antioxidative stress action. Progression of inflammation involving arteries is a crucial activator in pathogenesis of Takayasu arteritis (TA). Objective.-To investigate the relationship between serum bilirubin and TA. Design.-Our study involved 115 consecutive TA patients. Patients with active-phase disease were followed and received prednisone therapy. Results.-Lower concentrations of serum bilirubin were detected in TA patients compared with healthy subjects (0.6 +/- 0.31 versus 0.7 +/- 0.22 mg/dL, P = .02). Serum bilirubin concentrations in active TA patients were lower than those in inactive patients (0.5 +/- 0.20 versus 0.8 +/- 0.32 mg/dL, P >.001). In all patients with TA, serum bilirubin correlated positively with total protein (r = 0.193, P =.04) and negatively with C-reactive protein and erythrocyte sedimentation rate (r = -0.213, P = .03, and r = -0.532, P < .001, respectively). Multiple logistic regression analysis showed that each decrease of 1 mg/dL in serum bilirubin was associated with a 1.10 times increase in the odds for TA compared with the controls (odds ratio = 0.913, 95% CI, 0.856-0.974; P = .006). Serum bilirubin was correlated with erythrocyte sedimentation rate (beta = -0.170, P > .001) in multiple linear regression analysis. The area under the curve for serum bilirubin in predicting active TA patients was 0.802. Serum bilirubin levels were found to be significantly increased after prednisone treatment (0.5 +/- 0.20 versus 0.7 +/- 0.15 mg/dL, P = .002). Conclusions.-Lower serum bilirubin levels are associated with TA, and serum bilirubin may be influenced by prednisone therapy in active TA patients. Serum bilirubin levels in TA patients correlate negatively with erythrocyte sedimentation rate.