Korean modern medicine was imported from American missionaries in the late 19th century. At the beginning of the 20th century, Japanese medicine, which was influenced by German medicine, was imported along with the Japanese invasion. After the liberation of Korea, however, American medicine influenced the Korean Medicine in a broad spectrum: for example, medical science, medical instruments, and health care system. Not only an unstable social environment but also the rapid development of medical science changed medical terms. In order to investigate the 50-year transition of medical terms in Korea, we compare the names of diseases in 'Cho-Sŏn-Eu-Bo' published in 1934, 1935 and 1936 with those in the 'Journal of the Korean Medical Association' published in 1985. The names of diseases were classified according to number 17 classification method of ICD-9 (International Classification of Disease). The proportionate ratio of the number of names of diseases between 1935 and 1985 was 3.2 in neoplasms, 3.1 in diseases of the circulatory system, and 2.7 in mental disorders. The causes of the transition of the names of diseases were three. The first was the simple change of the rules of spelling, the second was the change of the concept of disease, and the third was the subdivision of diseases. 26.1% (N=37) of the names of diseases in 1935 (N=142) were changed by 1985.