In order to observe the frequency of visits and the distribution of endodontically treated patients according to age, sex, diagnosis, type of teeth, the author had surveyed the 17,250 outpatients of the Infirmary of the College Dentistry, Yonsei University from January 1976 to December 1978. 773 cases, 660 patients among 728 endodontically treated patients were studied. The obtained results were as follow; 1. The average frequency of visits were 5.95 in uppers and 5.88 in lowers. 2. The average frequency of visits were 5.79 in males and 6.02 in females. 3. At the age of under 14, the average frequency of visits were 7.42 in uppers and 6.76 in lowers. 4. According to diagnoses, the average frequency of visits in periapical granuloma or cyst were 2.80 in uppers and 3.16 in lowers. 5. The number of endodontically treated teeth had revealed as follow; upper incisors 27.94%, lower molars 25.87%, and upper molars 15.13% 6. The number of endodontically treated teeth by diagnoses were as follow; periapical abscess 45.27%, pulpit is 37.51%, tooth fracture 8.40%. 7. The number of endodontically treated teeth were 51.99% in the age of from 20 to 34.