We report clinical, radiographic and historical data on a large family with an unusually high prevalence of periodontitis. The proband, a 20-year-old black male, had the classic features of juvenile periodontitis (JP). His father was periodontally normal, while his mother had lost all her teeth at age 27 because of rapidly progressive periodontitis (RP). In addition to the 13 living children the couple had had 2 miscarriages. Of the children, one had RP, five had JP and two had prepubertal periodontitis (PP). Both maternal grandparents of the proband had become edentulous at an early age, presumably because of early-onset periodontitis. Four of 10 siblings of the proband's mother had early-onset periodontitis. In contrast, the paternal grandparents did not have early-onset periodontitis nor was periodontitis unusually prevalent in the siblings of the proband's father. The pedigree for this family is consistent with, but does not prove, an X-linked dominant pattern of genetic transmission. The natural history of early-onset periodontitis and the relationship among PP, JP and RP are not understood. The fact that the mother of the proband had RP and she had offspring with RP, JP and PP indicates a close relationship among these diseases and argues in favor of a common underlying mechanism. JP was not preceded by PP in the proband nor his affected 21-year-old brother, but one sister had PP, and at age 15 manifested JP. In her case, the alveolar bone around the deciduous molars had been destroyed, but it regenerated as the permanent premolars erupted.(ABSTRACT TRUNCATED AT 250 WORDS)