The present study has been performed to evaluate the clinical, microbiological, biochemical and immunological parameters associated with the periodontal disease activity in adolescent periodontitis. 21 young adolescents with evidences of periodontal attachment loss participated in the study for upto 3 years of examination. Probing pocket depths and attachment levels of whole dentitions were annually recorded and 4 deepest pockets, with initial probing depth ${geq}$ 4mm, were selected as the representative experimental sites of a patient. Sites experiencing attachment loss ${geq}$ 1mm during the 3-year experimental period were designated as the active sites and these sites were examined for the microbiological and biochemical profiles at the time when attachment loss occurred. Microbiological assay included cultural studies and PerioScan for monitoring BANA(+) organisms(e.g. Porphyromonas gingivalis, Treponema denticola, Bacteriodes forsythus). Biochemical assay has been performed for monitoring GCF levels of neutral protease. Serum IgG and IgG2 titers against Porphyromonas gingivalis 381 were determined of a patients at the beginning and the end of the study, respectively for patient-based analysis. The results indicated that the parameters consisting of microbiological cultures and GCF neutral protease exhibited low association with the periodontal disease activity in adolescents. However, the specificity for microbiological culture of the selected periodontopathic organisms(Aa,Pg,Pi) were considerably high. Moreover, the clinical pameters such as bleeding on probing and presence of plaque as well as IgG levels against Pg at the baseline exminations were closely associated with the subsequent evidences of attachment loss during the whole experimental period(3-year).