This study was performed to investigate the midline having the least difference between the right and left structure among the lines that had been used in the submentovertex analysis and secondarily to know the distribution of asymmetry and it´s degree existed normal persons and asymmetric patients. The subjects consisted of 40 normal adult patients and 40 asymmetric adult patients. The computerized anaylses from submentovertex cepholometric radiograph were carried out. The results were as follows ; 1. The right and left difference of the perpendicular bisecting line between right and left foramen spinosum was larger than the other midlines in the anterior area and it was decreased gradually as it progressed posteriorly. Specially the difference of this line was the smallest in the area where there was foramen spinosum. 2. The right and left difference of the perpendicular line through crista gali to the line between right and left foramen spinosum was smaller than the other midlines in the anterior area and it was increased gradually as it progressed posteriorly. 3. The right and left difference of the line between crista gali and anterior process of atlas was constant and smaller than the other midlines. 4. Asymmetry was a common finding in both normal and asymmetry group and left or right dominance of asymmetry was not statistically significant. 5. When the analyses were undertaken after submentovertex radiogram was divided into cranial base, upper face and lower face, the more inferior part showed relative asymmetry than the more superior part.