Introduction: Age estimation is one of the important issues for treatment planning and determination of patient’s rights in forensic medicine. In spite of various methods which have been introduced for age estimation, there is still no specific practical, non-invasive, and rapid method of age estimation for Iranian population. The aim of this study was to find a precise criteria for age estimation in Iranian native population based on the development of the maxillary and the mandibular third molar teeth. Methods: In this study 750 panoramic radiographs which were taken from 1993 to 2006 and belonged to healthy persons between 5.5-25 years old were collected in 5 different cities. Our criteria for selection of the cities was based on racial and geographic distribution and access to high amount of the cases. The cities were Isfahan, Ahvaz, Mashhad, Kerman and Tabriz. One hundred and fifty radiographs were collected from each city. The radiographs were randomly divided between two radiologists who independently evaluated the development of the mandibular and the maxillary third molar teeth based on Demergian calcification criteria. Statistical analysis was performed by Spearman and Pearson coefficient of correlations. Results: From 750 paranormic radiographs 535 (70%) and 215 (30%) belonged to females and males respecively. According to the results, in both genders, there is a significant difference between the upper and lower jaws regarding to the tooth development of the third maxillary molar (P<0.05). So that, upper third molars in male people were calcified faster in all Dermirgian phases in comparison with female ones. Conclusion: Demirgian formation stages is applicable for age estimation in Iranian population. The age of calcification was not similar in male and females that shows the role of gender on teeth calcification stage.