Polycystic ovary syndrome (PCOS) is associated with premature carotid atherosclerosis. C-Reactive protein (CRP) has been implicated as a vascular disease risk factor. The objective of this study was to determine whether elevated CRP is associated with increased carotid intima-media wall thickness (IMT) in PCOS women. Forty-seven PCOS patients and 59 similarly aged controls were screened for cardiovascular risk factors and concurrently underwent carotid ultrasonography (1996-1999). The main outcome measure was carotid IMT. CRP was significantly higher in PCOS patients than in controls (3.4 vs. 2.1 mg/dl; P = 0.002). In regression modeling, PCOS associated with IMT independently of CRP and age (P = 0.019). Body mass index reduced the association of PCOS and CRP with IMT and was also associated with IMT (P = 0.029). The CRP-IMT relationship was attenuated when either insulin or visceral fat was included in the PCOS-age-CRP model (P = 0.197 and P = 0.550, respectively). PCOS remained associated with IMT independent of insulin (P = 0.033) or visceral fat (P = 0.040). CRP does not appreciably mediate the effect of PCOS on IMT. Obesity partially explained the influence of PCOS and CRP on IMT. The effect of body mass index on the PCOS-IMT relationship was not completely determined by hyperinsulinemia or visceral fat, and might be mediated by other aspects of PCOS-related adiposity.