PURPOSE: This study was done to evaluate the efficacy of low-dose radiation in reduction of thoracic vertebral metastases in patients with breast cancer. MATERIALS AND METHODS: 109 patients who were treated for bone metastasis from breast cancer from June, 1988 to June, 1998 in the Department of Therapeutic Radiology, Seoul National University were included. Of the 109 patients, 40 patients had been previously treated by postoperative radiotherapy and 69 had not. Postoperative radiotherapy had been given using Co-60 teletherapy device in 30 patients or 6 MV linear accelerator in 10. Thoracic spines from 1 to 10 were usually irradiated except in 1 patient and cervical vertebrae 6 and/or 7 were partially included in 38 patients. A total of 50.4 Gy was given with 1.8 Gy fraction. Metastatic bone diseases were scored in 11 regions, i. e., skull, cervical spine, thoracic spine from 1 to 4, from 5 to 8, 9 and 10, 11 and 12, lumbar spine, pelvis, femur, ribs and others. RESULTS: In no postoperative parasternal irradiation group, lumbar vertebrae were the most common metastatic sites (55.1%) followed by pelvis (44.9%), ribs (40.6%), thoracic vertebrae 11 and 12 (37.7%), thoracic vertebrae between 5 and 8 (36.2%), thoracic vertebrae 9 and 10 (34.8%), and thoracic vertebrae between 1 and 4 (26.1%). In postoperative parasternal irradiation group, lumbar vertebrae and pelvis were also the most common sites of metastases (55.0% both) followed by ribs (37.5%), and thoracic vertebrae 11 and 12 (32.5%). But significant less metastases were seen at thoracic vertebrae from 1 to 10. CONCLUSION: We can find that there were significantly less bony metastases at thoracic vertebrae which had been previously irradiated postoperatively.