Frontal sinuses of Japanese skulls were radiographically examined from the view point of identifying individuals. The system of classification of sinus was proposed, basing on the area size, the bilateral asymmetry, the superiority of side, the outline of upper borders, the partial septa and the supraorbital cells. Frontal sinus patterns could be divided into above 20,000 possible combinations by combining the class numbers in each classification item described above. The frontal sinus pattern of a given person was formulated as a code number which was determined by arranging the class numbers in each classification item as serial numbers. This identification system by the frontal sinus pattern should allow one to characterize each person. The application of this identification system to an actual criminal case was also described.