The present study was undertaken to evaluate the change of circulating visfatin, C-reactive protein (CRP) concentrations, and insulin sensitivity in patients with hyperthyroidism. We studied 19 adult patients (14 women and 5 men aged 32.6 +/- 1.8 years) with hyperthyroidism due to Graves disease and 19 age- and sex-matched euthyroid controls (17 women and 2 men aged 36.7 +/- 2.7 years). All hyperthyroid patients were treated with 1 of 2 antithyroid drugs and were reevaluated after thyroid function normalized. Before antithyroid treatment, the hyperthyroid group had significantly higher visfatin plasma concentration (mean +/- standard error of the mean, 20.7 +/- 1.8 ng/mL) than the control group (16.2 +/- 1.3 ng/mL, P = .044); but the visfatin level dropped significantly after treatment (12.0 +/- 1.4 ng/mL, P < .001). The reciprocal index of homeostasis model assessment of insulin resistance (HOMA-IR) in the hyperthyroid group was higher before treatment (2.06 +/- 0.26 mmol mU/L*L) than after treatment (1.21 +/- 0.16 mmol mU/L*L, P = .027). There was no significant difference in serum glucose, high-sensitivity CRP, and insulin levels between hyperthyroid and control groups and in the hyperthyroid group before and after treatment. Body mass index-adjusted visfatin levels were significantly elevated in the hyperthyroid group. Pearson correlation revealed that visfatin, glucose, insulin, and HOMA-IR values positively correlated with triiodothyronine and free thyroxine levels. However, visfatin did not correlate with insulin and HOMA-IR levels. The results indicated that plasma visfatin concentration was elevated in hyperthyroidism due to Graves disease, but serum CRP levels were not. Plasma visfatin levels were not associated with indicators of insulin resistance in hyperthyroid patients.