Context Human adipose tissue expresses and releases the proinflammatory cytokine interleukin 6, potentially inducing low-grade systemic inflammation in persons with excess body fat. Objective To test whether overweight and obesity are associated with low-grade systemic inflammation as measured by serum C-reactive protein (CRP) level. Design and Setting The Third National Health and Nutrition Examination Survey, representative of the US population from 1988 to 1994, Participants A total of 16 616 men and nonpregnant women aged 17 years or older Main Outcome Measures Elevated CRP level of 0.22 mg/dL or more and a more stringent clinically raised CRP level of more than 1.00 mg/dL. Results Elevated CRP levels and clinically raised CRP levels were present in 27.6% and 6.7% of the population, respectively. Both overweight (body mass index [BMI], 25-29.9 kg/m(2)) and obese (BMI, greater than or equal to 30 kg/m(2)) persons were more likely to have elevated CRP levels than their normal-weight counterparts (BMI, <25 kg/m(2)). After adjustment for potential confounders, including smoking and health status, the odds ratio (OR) for elevated CRP was 2.13 (95% confidence interval [CI], 1.56-2.91) for obese men and 6.21 (95% CI, 4.94-7.81) for obese women. In addition, BMI was associated with clinically raised CRP levels in women, with an OR of 4.76 (95% CI, 3.42-6.61) for obese women. Waist-to-hip ratio was positively associated with both elevated and clinically raised CRP levels, independent of BMI. Restricting the analyses to young adults (aged 17-39 years) and excluding smokers, persons with inflammatory disease, cardiovascular disease, or diabetes mellitus and estrogen users did not change the main findings. Conclusion Higher BMI is associated with higher CRP concentrations, even among young adults aged 17 to 39 years. These findings suggest a state of low-grade systemic inflammation in overweight and obese persons.