This paper reports estimates of the periodontal status of US population derived from data from Phase 1 of the Third National Health and Nutrition Examination Survey conducted by the National Institute of Dental Research from 1988-1991. A total of 7,447 dentate individuals 13 years of age and older, representing approximately 160.3 million civilian non-institutionalized Americans, received a periodontal assessment. Measurements of gingival bleeding, gingival recession level, periodontal pocket depth, and calculus were made by dental examiners. Assessments were made at the mesiobuccal and mid-buccal sites of all fully erupted permanent teeth present in two randomly selected quadrants, one maxillary and one mandibular. All data were weighted and standard errors calculated by special software to adjust for the effect of sample design. Although over 90% of persons 13 years of age or older had experienced some clinical loss of attachment (LA), only 15% exhibited more severe destruction (LA > or = 5 mm). Prevalence of moderate and severe LA and gingival recession increased with age, while prevalence of pockets > or = 4 mm or > or = 6 mm did not. These data suggest that the increasing prevalence of LA with age is more associated with increasing prevalence of recession than with changes in the prevalence of pockets or age. The extent or number of affected sites with advanced conditions for loss of attachment, pocket depth, or recession was not large for any age group. Differences in prevalence of moderate and severe loss of attachment, moderate and deep pockets, and recession were found among gender and race-ethnicity groups. Females exhibited better periodontal health than males, and non-Hispanic whites exhibited better periodontal health than either non-Hispanic blacks or Mexican-Americans.