During the 15 month's period from July, 1970, until October, 1971, an epidemiologic study on chronic paranasal sinusitis was carried out with 5,489 Korean middle and high school students, i.e. 1,987 school boys and 455 night school girls from Seoul city, 756 school boys and 780 school girls from Che-Ju city, 390 school boys and 260 school girls from Cheong Ju city and 374 country school boys and 487 country school girls from Cheong Won county. This study covered the incidence of chronic paranasal sinusitis in respective area and the relationship between chronic paranasal sinusitis and environmental factors, subjective symptoms and its mental and physical effects. The obtained results were as follows : 1) The general incidence of chronic paranasal sinusitis in all of the groups was 16.0% and about two times greater incidence was observed in girls (22.0%) than in boys (12.6%). 2) The incidence of chronic paranasal sinusitis in each of 6 groups was between 8.8% and 33.3% and showed great differences among the groups. The incidence in groups of cities such as Seoul, Che Ju and Cheong Ju was between 8.8% and 22.6% and in the country areas, it was between 31.8% and 33.3%. As shown above, the incidence in country area was higher than in cities. 3) According to the study on dietary factors, the total amount of food intake and dietary unbalance showed no influence upon the incidence of chronic paranasal sinusitis. The intake amount of meat and fish was remarkable low in the group of patients with chronic paranasal sinusitis, compared with the normal population. Thus, it is presumed that the incidence of chronic paranasal sinusitis is influenced by the amount of intake of animal protein. 4) Comparing the group of patients of chronic paranasal sinusitis with the normal population regarding their house structures it is presumed that the incidence of chronic paranasal sinusitis is somewhat influenced by living condition, in other words, economic conditions and also by using water which is not hygienic and is contaminated, and by poor environmental hygiene which accompanies the habit of using unclean water. 5) There was a tendency for patients of chronic paranasal sinusitis to live in crowed rooms, which were poorly ventilated, dusty, not properly protected from the changing cold surrounding atmosphere or in room with unfaverable heating system. 6) The incidence of various subjective symptom was as follows : Headache 33.5% in males, 52.5% in females, rhinorrhea 45.9% in males, 48.7% in females, and nasal obstruction 48.6% in males, 41.1% in females. Thus, about half of the cases with chronic paranasal sinusitis showed subjective symptoms. The incidence of headache was much higher in females than in males. 7) Among the patients with chronic paranasal sinusitis, 41.6% of male patients and 48.4% of female patients were aware of the presence of paranasal sinusitis. On the other hand, among the normal population, 28.9% of males and 27.2% of females were mistaken in thinking themselves to be infected with chronic paranasal sinusitis, despite its absence. Nasal obstruction was the most important reason for considering themselves infected by chronic paranasal sinusitis, but memory disturbance was more important in males and headache was more important in females. 8) Chronic paranasal sinusitis showed no influence upon sleeping, physical activity or daily emotional moods, but the incidence of upper respiratory infection and fatigability was relatively high in patients with chronic paranasal sinusitis. 9) Reading and school activities were not influenced by chronic paranasal sinusitis but understanding ability and power of concentration showed tendency to decreased in the patient with chronic paranasal sinusitis. 10) Chronic paranasal sinusitis showed no effect on psychological aspects such as friendship, emotional irritability or endurance.