Many randomized clinical trials have been performed to address the effectiveness of postmastectomy radiation therapy (PMRT) to regional lymph nodes with or without chest wall irradiation. Although these studies have confirmed the usefulness of RT to reduce loco-regional recurrence, the benefit of postoperative RT for survival remains controversial. Recent prospective trials of PMRT in combination with systemic chemotherapy clearly demonstrated the benefit of this combined adjuvant therapy for both locoregional recurrence and survival outcomes. Based upon this new evidence, guidelines and recommendations for PMRT in the management of breast cancer have been proposed by the American Society of Clinical Oncology and by the International Consensus Panel at the International Conference on Adjuvant Therapy of Primary Breast Cancer in St. Gallen. PMRT is recognized as a standard adjuvant treatment for patients with more than 4 positive axillary nodes in these guidelines and recommendations. This re-appraisal of PMRT has not attracted much attention in Japan so far. Clinical studies are needed to determine how to best incorporate PMRT in the multimodal treatment of node-positive breast cancer.