The inclusion of occusal traits as part of the oral health component of the Third National Health and Nutrition Examination Survey, Phase 1, 1988-91, provided an opportunity to assess several occlusal characteristics in the US population: diastema > or = 2 mm, alignment of lower and upper anterior teeth, posterior crossbite, overbite, and overjet. Household questionnaires asked whether the individual had ever received orthodontic treatment. Prevalence of clinical measures of occlusal characteristics and orthodontic treatment was estimated for over 7,000 sample persons from 8 to 50 years of age, representing approximately 150 million non-institutionalized people in the United States. These findings present the first estimates of occlusal status of the US non-institutionalized population in more than 25 years. Eight percent of the population had severe overbite of 6 mm or more. The average overbite was 2.9 mm. Maxillary diastemas > or = 2 mm were observed in 19% of 8-11-year-olds, 6% of 12-17-year-olds, and 5% of adults 18-50 years old. Twenty-five percent and 22% of persons had zero mm of malalignment in maxillary and mandibular incisors, respectively. Conversely, 11% and 15% of persons had 6 mm or more displacement of maxillary and mandibular molars, respectively. Posterior crossbite affects less than 10% of this population, and less than 10% had overjet of 6 mm or more. Non-Hispanic black adults had the least amount of malalignment in mandibular incisors. Three times as many non-Hispanic blacks compared with non-Hispanic whites and Mexican-Americans had diastemas > or = 2 mm. Comparisons with published data from the National Health Examination Survey (1966-70) indicated a 20% increase of 12-17-year-olds with overbite in the normal range (0-3 mm). Almost 20% of adults ages 18-50, as well as 18% of children, have had orthodontic treatment.