The paper concerns the accuracy of two dental methods of age estimation based on the radiographic appearance of the root of the lower third molar. The first dental method tested was traditional with a subjective assessment of the root development stage and the second was a new method with a metric measurement of formed root length. Since previous studies have shown a relatively low precision for dentally based age estimation methods during adolescence, an additional independent indicator of chronological age was employed, namely skeletal maturity according to the atlas and method of Greulich and Pyle (Radiographic Atlas of Skeletal Development of the Hand and Wrist Stanford University Press, CA, 1959). The material was Swedish adolescents aged 12-19 years. It was found that all methods gave an overestimation of chronological age, with the highest overestimation, more than 1 year, for the two dental methods. A stepwise multiple regression analysis indicated that skeletal age alone explains 48% of the variation in estimated chronological age. It may be concluded that the accuracy of age estimations based on the lower third molars is quite uncertain during adolescence. Up to 18 years, it is preferable to use skeletal age alone as a predictor. Only a small increase in the explanation coefficient of age variation (3-4%) could be seen if digitized or subjectively estimated root lengths were added as predictors to the skeletal estimation.