A nation-wide survey on the prevalence and risk factors of chronic otitis media (COM) in Korea was conducted by means of physical examination by otolaryngologists from July to October, 1991. The total number of subjects examined was 9,321 drawn from 2,899 households residing in 60 different areas throughout the country. The overall prevalence rate of COM was 2.19%. For the study of risk factors of COM, a case-control analysis was made. The prevalence of COM varied neither by sex, nor by urban-rural difference. However, the risk increased with aging. There was a significant geographic variation by provinces. General risk factors such as crowding, economic activity, childhood home, marital status, maternal or paternal age, body weight, smoking habits, age of first otorrhea, preauricular fistula, canal atresia and cleft anomaly imply an increased risk of COM. Other factors such as residency, education, social class, height, history of breast feeding, microtia, nasal septal deviation, nasal polyposis and nasal allergic symptoms showed little influence on COM.