Context:​ The prevalence of obesity and overweight increased in the United States between 1978 and 1991. More recent reports have suggested continued increases but are based on self-reported data.

Objective:​ To examine trends and prevalences of overweight (body mass index [BMI] ≥25) and obesity (BMI ≥30), using measured height and weight data.

Design, Setting, and Participants:​ Survey of 4115 adult men and women conducted in 1999 and 2000 as part of the National Health and Nutrition Examination Survey (NHANES), a nationally representative sample of the US population.

Main Outcome Measure:​ Age-adjusted prevalence of overweight, obesity, and extreme obesity compared with prior surveys, and sex-, age-, and race/ethnicity–specific estimates.

Results:​ The age-adjusted prevalence of obesity was 30. 5% in 1999-2000 compared with 22. 9% in NHANES III (1988-1994;​ P<. 001). The prevalence of overweight also increased during this period from 55. 9% to 64. 5% (P<. 001). Extreme obesity (BMI ≥40) also increased significantly in the population, from 2.9% to 4.7% (P = . 002). Although not all changes were statistically significant, increases occurred for both men and women in all age groups and for non-Hispanic whites, non-Hispanic blacks, and Mexican Americans. Racial/ethnic groups did not differ significantly in the prevalence of obesity or overweight for men. Among women, obesity and overweight prevalences were highest among non-Hispanic black women. More than half of non-Hispanic black women aged 40 years or older were obese and more than 80% were overweight.

Conclusions:​ The increases in the prevalences of obesity and overweight previously observed continued in 1999-2000. The potential health benefits from reduction in overweight and obesity are of considerable public health importance.