PURPOSE: Although there are many reports on the development of paranasal sinuses, few studies were performed with respect to the frontal sinus with 3D CT, especially in Korean children. In this study, we evaluated the normal development of frontal sinus in Korean children with 3D CT imaging. METHODS: A total of 301 patients under the age of 20 were reviewed retrospectively. Maximal AP(anteroposterior) length, height and width were measured with the aid of computer device. The volume of frontal sinus was also evaluated. RESULTS: At the age of more than 4, the pneumatization of frontal sinus was detected. Frontal sinus developed continuously and was observed in almost every children at the age of more than 17. The AP length, height, width and volume of frontal sinus were enlarged continuously until the age of 20. And the maximal growth of frontal sinus was observed at puberty. The width and volume of frontal sinus showed high correlation coefficient(r=0.8) relative to height or AP distance. CONCLUSION: The results of this study may be helpful in the comprehension of normal development of frontal sinus in Korean children.