Hyperuricemia has recently been recognized to not only be a predictor of cardiovascular disease but also a marker of metabolic syndrome. We examined the association between uric acid levels and various clinical parameters, including the components of metabolic syndrome, in essential hypertension. One hundred forty-six untreated Japanese hypertensive patients (mean 58.3 years) without overt cardiovascular disease were divided into low and high uric acid groups by the median uric acid value (cut-off: 6.3 for men and 4.4 mg/dL for women). The high uric acid group had higher serum creatinine (0.74 vs. 0.67 mg/dL, p = 0.019) and a larger body mass index (BMI) (25.2 vs. 23.6 kg/m(2), p = 0.018) compared to the low group. Men from the high uric acid group were younger and had higher blood pressure (BP) than men from the low group. Uric acid levels were correlated with creatinine in both genders, with blood pressure, triglycerides in men only, and with BMI, fasting glucose in women only. Multiple regression analysis also indicated a significant correlation of uric acid with creatinine in both genders, with triglycerides in men, and with glucose in women. Metabolic syndrome (modified NCEP-ATPIII definition) was found in 37.0% of the high uric acid group (men 45.0, women 27.3%) and 20.8% of the low group. Results suggest that an increase of uric acid is associated with impaired renal function and constitutes a risk factor for metabolic syndrome. Uric acid may also be a useful index for initial risk stratification of untreated patients with essential hypertension.