Context: Overweight and obesity are increasing dramatically in the United States and most likely contribute substantially to the burden of chronic health conditions. Objective: To describe the relationship between weight status and prevalence of health conditions by severity of overweight and obesity in the US population. Design and Setting: Nationally representative cross-sectional survey using data from the Third National Health and Nutrition Examination Survey (NHANES III), which was conducted in 2 phases from 1988 to 1994. Participants A total of 16 884 adults, 25 years and older, classified as overweight and obese (body mass index [BMI] ≥25 kg/m2) based on National Institutes of Health recommended guidelines. Main Outcome Measures: Prevalence of type 2 diabetes mellitus, gallbladder disease, coronary heart disease, high blood cholesterol level, high blood pressure, or osteoarthritis. Results: Sixty-three percent of men and 55% of women had a body mass index of 25 kg/m2 or greater. A graded increase in the prevalence ratio (PR) was observed with increasing severity of overweight and obesity for all of the health outcomes except for coronary heart disease in men and high blood cholesterol level in both men and women. With normal- weight individuals as the reference, for individuals with BMIs of at least 40 kg/m2 and who were younger than 55 years, PRs were highest for type 2 diabetes for men (PR, 18.1; 95% confidence interval [CI], 6.7-46.8) and women (PR, 12.9; 95% CI, 5.7-28.1) and gallbladder disease for men (PR, 21.1; 95% CI, 4.1-84.2) and women (PR, 5.2; 95% CI, 2.9-8.9). Prevalence ratios generally were greater in younger than in older adults. The prevalence of having 2 or more health conditions increased with weight status category across all racial and ethnic subgroups. Conclusions: Based on these results, more than half of all US adults are considered overweight or obese. The prevalence of obesity-related comorbidities emphasizes the need for concerted efforts to prevent and treat obesity rather than just its associated comorbidities.