Although there are many reports on the measurement of the paranasal sinuses, few studies examined the development of frontal sinus with three-dimensional computed tomography (CT), especially in children. In this study, we evaluated the normal development of frontal sinus in Asian children, and we also analyzed the height, length, and width of the frontal sinus in Korean adults with three-dimensional CT imaging. We retrospectively reviewed three-dimensional facial bone CT of a total of 352 patients younger than 23 years. The occurrence of the frontal sinus was evaluated by their age. The maximal length, height, and width were measured with a computer device. The volume of the frontal sinus was also evaluated. In those older than 4 years, the pneumatization of frontal sinus was detected. Frontal sinus developed continuously and was observed in almost every child older than 17 years. The length, height, width, and volume of the frontal sinus continuously increased until the age of 20. The maximal growth of the frontal sinus was observed at puberty. The width and volume of the frontal sinus showed a high correlation coefficient (r=0.8) relative to the height or length. In adults, the mean height, width, depth, and volume of the frontal sinus were 27.2±7.0 mm, 52.5±17.1 mm, 22.0±6.3 mm, 8.39±3.78 cm, respectively. The results of this study may be helpful in understanding the normal development of frontal sinuses in children. It could be also helpful for further research and surgical approaches for frontal sinuses.