For the forensic odontologist, reliability and adequate precision of age determination by using third molars is critically important. Uncertainties emerge primarily from the biological variability of the third molars among all the permanent teeth and also from the significant individual differences in the developmental pattern of the wisdom teeth. Discrepancies have also been found between the growth of the maxillary and the mandibular third molars. Moreover, variable estimates of dental age as well as different frequencies of agenesis have been reported between ethnic groups. In order to obtain reference material on the third molar development of Japanese juveniles for use in forensic applications in Japan, the current study performed observations on the orthopantomograms of 1,282 Japanese dental patients between the ages of 14 and 24. Demirjian formation stages of the maxillary and mandibular third molars were recorded for chronological evaluation of wisdom teeth and applied for further statistical analysis. The analysis found statistically significant differences between the upper and lower jaws and between genders. Males achieved root developmental grades earlier than females. The study assessed the mean ages for all formation grades and predicted the probability that a Japanese juvenile would be older than the relevant ages of 14, 16, and 20 as defined by Japanese juvenile law. The determined probability of a Japanese individual being younger or older than the relevant age cut points established for distinguishing between a juvenile and adult for criminal justice processing might be valuable in future forensic practice. Also, since the age for legal prosecution varies among countries, the assessment of the probability of a Japanese youth being older than 18 years may prove to be a useful forensic tool outside of Japan. 5 tables, 2 figures, and 22 references