Background/Aims: Insulin resistance is associated with serum C-reactive protein (CRP) levels. We aimed to evaluate the effect of bicalutamide on insulin resistance and serum CRP levels in non-obese polycystic ovarian syndrome (PCOS) patients. Methods: 40 non-obese patients (BMI ≤25 kg/m<sup>2</sup>) with PCOS and, 40 age- and BMI-matched healthy women were studied. Patients received bicalutamide orally at the dose of 25 mg/day. Serum CRP levels were measured with immunometric assay. Homeostasis model assessment (HOMA-IR) index was used for insulin resistance. Results: Mean Ferriman-Gallwey score (FGS) (p = 0.001), insulin (p = 0.001), serum glucose (p = 0.001), prolactin (p < 0.003), total (p < 0.04) and free testosterone (p = 0.001) and free androgen index (FAI) levels (p = 0.001) of PCOS subjects were higher than in the control group. Mean HOMA-IR of PCOS patients was higher than in control subjects (2.43 ± 1.2 and 0.94 ± 0.37, p = 0.001). CRP levels in subjects with PCOS was also higher than in control subjects (4.27 ± 1.33 and 0.98 ± 0.19, p = 0.001). After bicalutamide treatment, FGS, free and total testosterone and FAI decreased (p = 0.001). HOMA-IR, prolactin and CRP levels did not show any statistical difference with bicalutamide treatment. Conclusions: PCOS patients had insulin resistance and a high CRP level. Bicalutamide treatment did not influence insulin resistance and CRP level in PCOS, and this ineffectiveness of bicalutamide on CRP levels may be the result of insulin resistance and/or high prolactin levels at this time.