The aim of this study was to determine the effect of metabolic syndrome on brachial-ankle pulse wave velocity (baPWV) by using the new guidelines for diagnosis of this syndrome in Japan. We examined 525 men and women without a history of cardiovascular disease or cancer, and an ankle-brachial index < 0.9. The baPWV was measured using a device (Form PWV/ABI) that simultaneously monitored bilateral brachial and ankle pressure wave forms. Metabolic syndrome was defined as a waist circumference > or = 85 (90) cm in men (women) and two or more of the following risk factors: hypertension, dyslipidemia, and glucose intolerance diagnosed by a 75 g oral glucose tolerance test. The baPWV showed a significant linear relationship with waist circumference, waist-to-hip ratio, body fat, systolic and diastolic blood pressure, triglycerides, fasting glucose, 2-h-postload glucose, fasting insulin, and glycosylated hemoglobin-A1c, after adjusting for sex and age. These factors were also strongly related to fasting insulin levels. When subjects were classified into six groups based on waist circumference and the number of risk factors for metabolic syndrome (0, 1, and > or =2), we found that more risk factors clearly increased the odds ratios for an elevated baPWV in those subjects in the highest quartile of the baPWV distribution in multivariate logistic models. An increase in odds ratio was observed despite a normal waist circumference and may well have been due to increased fasting insulin and blood pressure levels. An increase in the number of risk factors for metabolic syndrome was highly correlated with an increased baPWV, probably due to insulin resistance.