AbstractThe aims of this study were (1) to monitor the progression and patterns of progression of loss of attachment ≥1 mm on a site basis over a 5‐year period in adolescents, and (2) to relate the presence of oral deposits and inflammation to the subsequent development and progression of loss of attachment on a site basis. 167 subjects were examined at ages 14, 16 and 19 years. Loss of attachment ≥1 mm, plaque, subgingival calculus, gingival bleeding and gingival colour change were assessed on the mesiobuccal sites of the 1st molars, 1st premolars and central incisors. Each site was treated separately in the analysis to avoid the problem of within‐subject site dependence. Sites were classed as progressing, non‐progressing or fluctuating according to the probing attachment level measurements at each of the 3 examinations. During the 5 years of this study, a total of 542 sites in 128 subjects progressed: 1136 sites in 162 subjects did not progress; 43 sites in 30 subjects had fluctuating attachment level measurements. Sites which subsequently progressed had significantly more plaque, subgingival calculus and gingival inflammation than non‐progressing sites at the baseline examination and throughout the study (p<0.001). Between 55‐57% of the maxillary 1st molars and 46‐49% of the mandibular incisors progressed. In contrast, there was no progression of loss of attachment on over 80% of the maxillary central incisors and mandibula