A National Survey of the Oral Health of U.S. children aged 5 to 17 was conducted by the National Institute of Dental Research during the 1986-87 school year. Eleven thousand and seven adolescents aged 14 to 17 years received a periodontal assessment. Their patterns of loss of periodontal attachment as assessed by probing at mesial sites were used to classify adolescents as cases of early onset periodontitis. Approximately 0.53% of adolescents nation-wide were estimated to have localized juvenile periodontitis (LJP), 0.13% to have generalized juvenile periodontitis (GJP), and 1.61% to have incidental loss of attachment (LA) (greater than or equal to 3 mm on 1 or more teeth). The total number of adolescents affected were not trivial. Close to 70,000 adolescents in the U.S. were estimated to have LJP in 1986-87. More destructive GJP affected an estimated 17,000 adolescents. Another 212,000 adolescents were estimated to have incidental LA. Blacks were at much greater risk for all forms of early onset periodontitis than whites. Males were clearly more likely (4.3 to 1) to have GJP than females when other variables were statistically controlled. Gender associations were more complicated for LJP because gender interacted with race. Black males were 2.9 times as likely to have LJP as black females. In contrast, white females were more likely than white males to have the disease by about the same odds. When interactions among demographic variables exist, caution must be taken in comparing results from different studies.