The system for classification of sinuses was proposed, based on the area size, the bilateral asymmetry, the superiority of side, the outline of upper borders, the partial septa, and the supraorbital cells. The frontal sinus pattern of a given person was formulated as a code number with seven figures determined by assigning the class number, according to the characteristics for each classification item described above. By arranging the class number as serial numbers, frontal sinus patterns could be theoretically divided into more than 20,000 possible sets of code numbers. In order to evaluate the reliability of this identification system, each radiograph was compared to 100 other samples. The result indicated that the individualization was possible on 4944 out of 4950 individual comparison cases by the code number of frontal sinus patterns alone. This identification system, therefore, should allow one to characterize each person. The application of the identification system to an actual criminal case is also described. 5 tables, 4 figures, 55 references. (Publisher abstract)