It has been generally recognized that the radiological appearances of cysts and tumors related to an embedded tooth are similar. However, based on their clinical experience, Abrams et al. pointed out that there was a difference between the two lesions at the attachment point to the embedded tooth. To investigate this difference, we conducted a study employing the radiographs of patients who visited Nihon University Dental Hospital at Matsudo and were pathologically defined as having a cyst or tumor. Using radiographs of these patients, we investigated the attachment point to the embedded tooth, and expressed the results as the proportion of the attachment point to the embedded tooth root length. The study was carried out in 100 patients with cysts (87 dentigerous cysts and 13 odontogenic keratocysts), and 27 patients with benign tumors (24 ameloblastomas and three adenomatoid odontogenic tumors). Prior to treatment based on the numerical results, the distribution of the results was examined. Thus, we evaluated several methods of examining the distributions, and found the best method to be discriminant analysis. The results showed that the discriminated boundary value (from the cemento-enamel junction) was 0.38 for the embedded tooth root length. The cases showing a boundary value of less than 0.4 for the cemento-enameljunction were judged to be cysts, and those showing a value of 0.4 or more were judged to be benign tumors. The rate of misjudgement was 28 % in the cyst group and 33.3 % in the benign tumor group.