Juvenile periodontitis occurs in children and young adults and can be classified into: periodontitis which occurs in otherwise healthy individuals, and periodontitis which occurs in juveniles with systemic disease. The periodontitis which occurs in otherwise healthy individuals consists of two major forms: juvenile periodontitis, also called periodontosis or localized juvenile periodontitis (LJP), and generalized juvenile periodontitis which includes early onset adult periodontitis, recurrent necrotizing ulcerative periodontitis and the true generalized form of juvenile periodontitis. Periodontitis in systemically diseased individuals can be divided into three subgroups: juvenile periodontitis associated with primary neutrophil disorders, juvenile periodontal disease in which neutrophils are secondarily abnormal, and juvenile periodontitis associated with other diseases. Juvenile periodontitis is perhaps the best understood form of periodontal disease. A major infecting organism, Actinobacillus actinomycetemcomitans, is strongly associated with the disease, and may be an exogenous pathogen since it is not found in healthy individuals or in healthy sites in LJP patients. It is virulent with marked leukaggressive properties and it induces a marked antibody response in infected patients. Eradication of Actinobacillus actinomycetemcomitans requires attention to the fact that it invades the tissue and hence systemic antimicrobials or surgical excision of the tissues is necessary for eradication. Marked suppression of the organism from subgingival sites is associated with healing. Host responses in LJP have also been well described and most immune functions studied appear to be normal. The notable exception is neutrophil chemotaxis which is depressed. Associated with depressed neutrophil chemotaxis is a reduction of neutrophil receptors for several chemotactic factors including C5a, the fifth component of complement.