Obesity and overweight have been associated with increased carotid intima-media thickness and stiffness in adults and children. Overweight and obesity have also been associated with an increased prevalence of the metabolic syndrome (MS). The aim of the study was to test the hypothesis that obese children with the MS have increased rigidity of their arteries compared with obese children without the MS. We studied 100 obese children (age range 6 to 14 years; 61 males, 39 females) consecutively seen in the outpatient clinic of a hospital department of pediatrics. Anthropometric measures and biochemical tests were performed in all children. Quantitative B-mode ultrasound scans were used to measure intima-media thickness and diameters of the common carotid artery. Common carotid arterial stiffness was significantly higher in the group of obese children with the MS (n = 38) at 1.29 +/- 0.06 mm (values log transformed) versus 1.12 +/- 0.04 mm (p <0.03) compared with those without the MS (n = 62). These differences persisted even after adjustment for age, gender, and C-reactive protein. Obese children with the MS had significantly higher plasma concentrations of C-reactive protein (1.57 +/- 0.06 microg/L, values log transformed) compared with obese children without the MS (1.38 +/- 0.05 microg/L, p <0.03). In conclusion, obese children who met the diagnostic criteria for the MS had higher common carotid artery stiffness and higher C-reactive protein plasma concentrations than obese children without the MS.