62 patients of histologically proven post-mastectomy case of breast cancer who was treated by radiation therapy from Nov. 1969 to Sept. 1963 at Yonsei Cancer Center, was reviewed in respect to the primary tumor, method of radiation therapy and the extend of effect of radiation therapy in the view of prognosis and its complication. 1. The peak age incidence was at the 4th decade (40.3%), and the next was 5th decade (32.3%) 2. The location of the primary tumor site was most frequent at the upper outer quadrant of the involved breat (44%) 3. By UICC staging, stage III of advanced case was relatively frequent (45.2%) that suggests no early detection of the breast cancer. 4. Except 2 patients of inoperable cases, remaining 60 patients received radiation therapy after mastectomy. Although the radiation therapy source and method are somewhat different, average 4000-5000 rads/4-5 wks were given to the peripheral lymphatics. 5. 30 cases were followed up among 62 patients. One year survi als were 25/30 cases(83.3%), 2 years were 10/13 cases(71%), 3 years were 8/11 cases and 4 year survivals were 2/3 cases. 6. Leukopenia (below 4000m㎥) during radiation therapy was noted in 57% of the cases, especially in the case of large radiation field and who received therapy by the conventional 250KV orthovoltage X-ray unit on the chest wall. 7. Skin reaction during radiation therapy was noted in 9 cases, and they were treated by conventional 250KV orthovoltage unit. 8. Local recurrence or metastasis was noted in 20 cases and 11 cases were stage III, and 10 cases were young age group below 35. Most frequent site of recurrence or metestasis was lung and pleura(9), and other site was chest wall (5), supraclavicular lymph node (5), bone (4) and to the opposite breast (2). 9. Deceased patient was 5 cases. Among them, 4 cases were advanced stage III and IV, and delayed visit to the hospital after the discovery of breast mass and further delaying in radiation therapy after mastectomy.