To determine the prevalence of metabolic syndrome among patients with gout and to examine the association between the 2 conditions in a nationally representative sample of US adults. Using data from 8,807 participants age >or=20 years in the Third National Health and Nutrition Examination Survey (1988-1994), we determined the prevalence of metabolic syndrome among individuals with gout and quantified the magnitude of association between the 2 conditions. We used both the revised and original National Cholesterol Education Program Adult Treatment Panel III (NCEP/ATP III) criteria to define metabolic syndrome. The prevalence (95% confidence interval [95% CI]) of metabolic syndrome according to revised NCEP/ATP III criteria was 62.8% (51.9-73.6) among individuals with gout and 25.4% (23.5-27.3) among individuals without gout. Using 2002 census data, approximately 3.5 million US adults with a history of gout have metabolic syndrome. The unadjusted and age- and sex-adjusted odds ratios (95% CI) of metabolic syndrome for individuals with gout were 4.96 (3.17-7.75) and 3.05 (2.01-4.61), respectively. With the original NCEP/ATP criteria, the corresponding prevalences were slightly lower, whereas the corresponding odds ratios were slightly higher. The stratified prevalences of metabolic syndrome by major associated factors of gout (i.e., body mass index, hypertension, and diabetes) remained substantially and significantly higher among those with gout than those without gout (all P values <0.05). These findings indicate that the prevalence of metabolic syndrome is remarkably high among individuals with gout. Given the serious complications associated with metabolic syndrome, this frequent comorbidity should be recognized and taken into account in long-term treatment and overall health of individuals with gout.