The author observed the relationships beween the dental midline and the midsagittal plane by taking 242 cases P-A cephalo-graphy grouped by male and female 2-6 years age group, 7-15 years age group, and adult age group. The following results were obtained by the observation. 1. Generally, the median line almost coincided with dental midline ineach age group. 1. It showed som degree of deviation in each age group. 2. It showed some degree of deviation in each age group. 3. The some degree of deviation shifted in accordance with each age group. 4. In adult age group, the dental milline more coincided with median line in male than in female.