A study of the prevalence of early onset periodontitis in U.S. children aged 14 to 17 years has been completed and will be published in October, 1991. A major contract to relocate, reexamine and collect risk factor information on these children will begin in October, 1991. Research objectives are to: a) assess the progression of periodontal destruction among the cases of early onset periodontitis, b) characterize the microbial ecology of the sub-gingival plaque among persons with early onset periodontitis, c) describe periodontal destruction and the presence of biologic and non-biologic putative risk markers among the probands' similar aged siblings, and d) compare the presence and concentration of selected putative pathogens and host- resistance factors among individuals with early onset periodontitis to controls.