['To determine the level of plasma soluble CD40 ligand (sCD40L) in patients with polycystic ovary syndrome (PCOS).', 'Prospective study.', 'Baskent University School of Medicine in Turkey.', 'Thirty-one patients with PCOS and 31 non-PCOS (control) patients.', 'Determination of plasma sCD40L and homocysteine levels.', 'Plasma sCD40L, fasting glucose, fasting insulin, homeostatic model assessment insulin resistance index (HOMA-IR), LH, FSH, E(2), total T, DHEAS, total cholesterol, high- and low-density lipoprotein cholesterol, triglyceride, homocysteine, and high-sensitivity C-reactive protein (hsCRP).', 'The mean serum fasting insulin and HOMA-IR levels were significantly higher in the PCOS group. The mean serum homocysteine level was significantly higher in the PCOS group. Despite a trend for higher high-sensitivity C-reactive protein levels in the PCOS group, the difference did not reach statistical significance. The mean plasma sCD40L level in the PCOS group was significantly higher than that in the control group (5.14 +/- 3.65 ng/mL vs. 3.45 +/- 2.64 ng/mL, respectively).'] Is polycystic ovary syndrome associated with elevated plasma soluble CD40 ligand , a marker of coronary artery disease?