The objective of this research was to estimate the prevalence of weight misperception among adults using the most recent nationally representative data, according to measured weight category and to assess the relationship between weight misperception and race/ethnicity. Height and weight were measured as part of the 1999-2006 National Health and Nutrition Examination Survey. The study sample consisted of 17,270 adults aged >or=20 years. BMI was categorized as underweight (BMI < 18.5), healthy weight (18.5 </= BMI < 25), overweight (25 <or= BMI < 30), and obese (BMI >or= 30). Subjects reported self-perception of weight status. Among study subjects, 31.7% of healthy weight adults, 38.1% of overweight adults, and 8.1% of obese adults incorrectly perceived their weight category. Among obese men, the odds of weight misperception were higher for non-Hispanic blacks (odds ratio (OR) = 3.0; 95% confidence interval (CI) = 2.0-4.5) compared to non-Hispanic whites and for persons with less than a high school education (OR = 2.1; 95% CI = 1.3-2.1), compared to those with some college education. Among obese women, the odds of weight misperception were higher for non-Hispanic blacks (OR = 3.4; 95% CI = 1.4, 3.1) and Mexican Americans (OR = 1.9; 95% CI = 1.2, 3.2) compared to non-Hispanic whites and for persons with less than high school education compared to those with some college education (OR = 5.5; 95% CI = 3.3-9.3). Weight misperception is highly prevalent in the US population, and more frequent in racial/ethnic minorities, males, and in persons with lower educational levels. Addressing the issue of weight misperception may help address the problem of obesity in the United States by increasing awareness of healthy weight levels, which may subsequently have an impact on weight-related behavior change.