Periodontal disease progression was studied on bitewing radiographs taken at baseline and after 1 year for a group of 422 teenagers who had no access to preventive or therapeutic dental services. Subjects exhibiting one or more proximal surfaces of 1st molars with longitudinal bone loss and/or with vertical bone defects at the 2nd examination were regarded as periodontal risk patients. This group then underwent a further examination in which periapical radiographs of the anterior teeth were taken and the clinical loss of attachment at the proximal surfaces of all teeth was assessed. Subsequently, the radiographic and clinical states of the risk group were compared. Most sites exhibiting bone loss during the study period displayed vertical bone defects and were largely confined to mesial surfaces of first molars. 24% of sites showing alveolar bone loss at baseline demonstrated further loss 1 year later. Girls exhibited significantly higher prevalence and incidence of sites showing bone loss than did boys. 24 children (5.7%) were regarded as periodontal risk patients. The radiographs significantly underestimated the prevalence of periodontal destruction in the risk group as compared to clinical measurements. It was concluded that using 2 bitewing radiographs is adequate for the identification of risk subjects, and that periodontal progression in adolescence occurs mainly in the first molar region and may affect girls more often than boys.