AbstractA cross‐sectional epidemiologic survey was conducted of 618 Navajo Indians, aged 14–19, resident in a boarding school in New Mexico. Periodontal status was assessed by clinical measurements of attachment level and gingival bleeding, and evidence of alveolar bone loss from standardized bitewing radiographs. Attachment level and gingival bleeding were measured at 24 posterior interproximal sites (six sites in each quadrant): the mesio‐buccal aspect of the second molar; the disto‐buccal and mesio‐buccal aspects of the first molar and second premolar; and the disto‐buccal aspect of the first premolar. Alveolar bone level was measured from radiographs at the corresponding approximal surfaces of the same teeth. Attachment loss was considered present when the distance from the CEJ to the base of the pocket was>1 mm; bone loss was considered present when the radiographic distance from the CEJ to the alveolar crest was>2 mm, and gingival bleeding was considered present if bleeding occurred immediately after gentle probing. Attachment loss was evident at one or more sites in 88.7% of the population, 45.9% of the subjects had attachment loss at eight or more sites, and 101 subjects (16.3%) had one or more sites with at least 4.0 mm of attachment loss. Bone loss was present at one or more sites in 89.2% of the population, 28.6% had eight or more affected sites, and 4.7% (29 subjects) had one or more sites with at least 2.0 mm of bone loss. Gingival bleeding was evident at one or more sites in 70.6% of the population, and 19.7% had eight or more affected sites. None of the conditions were strongly associated with sex, but the prevalence of bone loss increased with age. The prevalence and severity of incipient periodontitis seemed much higher in these subjects than previously reported in other adolescent groups when similar diagnostic criteria and methods of measuremen