We studied the periodontal disease progression and the relationship between some forms of destructive periodontitis in a group of Brazilian adolescents with high prevalence of periodontal destruction, and evaluated the adequacy of reducing data by limiting the measurement of disease to first molars and by aggregating and pooling site-scores into subject-level scores. Over a period of 3 years 222 adolescents were examined annually by bite-wing radiographs. Individuals displaying arc-shaped bone lesions adjacent to greater than or equal to 2 first molars were diagnosed as juvenile periodontitis (JP) patients, while those with greater than or equal to 1 first molars showing vertical lesions were regarded as periodontal risk subjects. Teenagers with greater than or equal to 2 first molars exhibiting longitudinal bone loss were defined as high-risk patients. At the ages of 13 and 16 years, 3 (1.3%) and 4 (1.8%) subjects had JP, while 12 (5.4%) and 28 (12.6%) were regarded as periodontal risks; 8 (3.6%) subjects were assigned to the high-risk group; 4 (1.8%) 13-year olds had greater than or equal to 1 first molars missing; hence, no loss of posterior teeth occurred over a period of 3 years. Analyzing the data at the site-level revealed progressive loss and little fluctuation in the alveolar bone height in the high-risk group, and a more pronounced bone loss at the mesial than at the distal surfaces. Simpler data sets were constructed by aggregating some of the site-scores or by pooling these into subject-level scores.(ABSTRACT TRUNCATED AT 250 WORDS)