We will analyze the cost-effectiveness of alternative age-specific frequencies with which different types of dental x-rays are performed. We will initially focus on the use of x-rays to detect carious lesions in children and adolescents. The analysis will consider, as a function of x-rays frequency, the trade-off between dollar costs and possible radiation hazards versus the status of carious lesion or other disease at the time of detection. Despite the low cost per x-ray, almost 800 million dollars per year are spent on dental x-rays. When one considers that a large number of people receive little dental care, the cost of dental x-rays if all people received adequate dental care would be significantly higher. Further, though radiation risks from dental x-rays appear low, uncertainty surrounding parameters used to estimate the effect of low radiation doses suggests all exposure to radiation be balanced against potential benefit. Thus, analysis of the cost-effectiveness of alternative frequencies seems important. We are not aware of any previous such analysis. Analysis of the effect of alternative frequencies requires consideration of questions like the following: "if an x-ray had been performed six months later, how much further would a carious lesion or other disease detected by the x-ray have progressed?" Our approach to considering this type of question will be to develop and validate a model of the initiation and progression of the disease. The model will be developed from longitudinal data and validated using cross-sectional prevalence data. By superimposing alternative x-rays frequencies on the model, we will be able to determine effect of alternative frequencies on the status of the disease at the time of detection. This will be compared to the costs of the x-rays.