This study was performed to investigate the factors concerning the structures of diseases in Korea. The data were collected from the 11 tertiary referral hospitals and the number of investigated patients were 242.038 and the diagnoses were based on 21 chapters of Korean Standard Classification of Diseases(KCD-3). The results were as fellows: 1. The number of investigated patients were 242,038 Among them male(51.1%) was a little more than female 48.9%). In age distribution, the group of 45-64 was the highest(25.5%) and 30-49year age group was 20.9%. under l4year age group was 20.3%. and above 65years age group was the lowest( 15.3%). 2. In single diagnosis group division by 21 chapters of KCD-3. diseases of the respiratory system were the highest(11.3%) , injury. poisoning and the next were certain other consequences of external causes( l0.39% ) and neoplasms(10.0%) . The low est were diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism(0.7%). in single diagnosis group, sex, age. season, region and operation and procedures were statistically significant in the ×2-test analysis. 3. In multiple diagnoses group. neoplasms were the highest (17.0%). and the next were pregnancy, chirdbirth and the puerperium(l0.6%) and the diseases of the circulatory systems(9.2%). The lowest was diseases of the blood and blood forming organs and certain disorders involving the immune mechanism(0.6%). In multiple diagnoses group, sex. ace. season, region and operation and procedures were statistically significant iii the ×2-test analysis.