Body mass index (BMI; kg/m2) distributions are commonly reported in the scientific literature to describe weight for stature. These data are collected for various groups of subjects in local health and body composition studies, and comparisons with national distributions are often desirable. Tabular data for population prevalence estimates from the third National Health and Nutrition Examination Survey (NHANES III, 1988 to 1994) at selected gender- and age-specific BMI levels ranging from < 18.0 to > 45.0 are presented and compared with various examples of BMI criteria reported in the scientific literature. NHANES III was a statistically representative national probability sample of the civilian, noninstitutionalized population of the United States in which height and weight were measured as part of a more comprehensive health examination. The implications of varying population prevalence estimates based on varying BMI cutoff points are briefly discussed for selected examples including World Health Organization over-weight/obesity criteria and the U.S. Dietary Guidelines for Americans. The median BMI for U.S. adults aged 20 years and older is 25.5 kg/m2. Median stature and weight for men are 175.5 cm and 80.0 kg and for women are 161.6 cm and 65.6 kg, respectively. The percentage of the population with BMI < 19.0 is 1.6% for men, 5.7% for women; BMI > or = 19.0 to < 25.0 is 39.0% for men, 43.6% for women; BMI > or = 25.0 is 59.4% for men, 50.7% for women. An estimated 97.1 million adults have a BMI > or = 25.0. Additional prevalence estimates based on other BMI cutoff points and ages are presented.