In radiation therapy, a complete study of patients on the indication of radiotherapy, delicate consideration during the radiotherapy, adequate after-care, the follow-up study and reconsideration are necessary. It takes, time to evaluate. Sometimes the misjudgement of patients last several years. However, the great endurance and efforts are vital necessity for the radiotherap evaluation and improvment of radiotherapy techniwus. At the Radiological research institute, all the radiotherapy patients from November 23, 1963 to December 31, 1968 were observed, and among them, those who survived three years after radiotherapy were analyzed in order to report the difficulty in follow-up study and to help formulate a better method of radiotherapy. All the follow-up study was done by questinaire form. We have sent 8,470 letters, and received 2,084 Positive answers and the returned and no-reply were 6,386. As a sample case, 121 patients, who reside in Chongro-ku Seoul, were selected for home-visiting by our staffs. 67 patients could he located easily where as 71 patients could not be located. The results of follow-up correspondences were analyzed and categorized by the international clacification of disease. Three-year survivors an the surviving rate are listed.