The purpose of this study was to investigate the interrelationship of the experimental group and control group by analyzing case histories, intraoral radiographs, orthopantomographs, intraoral slide films and dental casts. The date for this study were complied from 654 outpatients of the Department of Orthodontics, Seoul National University Hospital. The following conclusions were obtained. 1. When one or more third molar teeth were congenitally missing, the incidence of the other congenitally missing teeth was high. 2. The frequency of congenitally missing teeth was comparatively higher in male, maxilla, class II and class III. 3. The congenitally missing area of the third molar by Angle´s classification was not significant. 4. The order of frequency of congenitally missing teeth was the third molar, the second premolar, the lateral incisor, the first premolar, the first premolar, the central incisor, the canine, the first molar, the second molar.