Purpose: To evaluate the role of postoperative radiotherapy [PORT] after mastectomy for the breast cancer patients with parasternal lymphnodes [PSLN] metastases proven by biopy during the operation.Materials [amp ] Methods: Between 1985.9 and 1993.9, 150 breast cancer patients with parasternal lymphnodes metastases were randomized into 3 groups during the operation, Group 1 :radical resection of PSLN and supraclavicular lymphnodes [SCLN], Group 2 : Irradiation of 42 Gy/4.5 weeks to PSLN and SCLN regions, Group 3 : sampling of PSLN without further treatment as a control. All 3 groups of patients received 6 courses of CMF(cyclophosphamide, methtrexate, 5Fu) as adjuvant chemotherapy. Patients with high age (over 70), noninvasive carcinoma, inflammatory carcinoma and with distant metastases were excluded from this study.Results: The 5 years disease free survival (DFS) in the 3 groups were Group 1: 57%, Group 2: 53%, Group 3: 51%, respectively. The incidence of distant metastases such as distant lymphnodes, bone and visceral metastases were same in the groups (Group 1 : 1550, Group 2 : 1550,, Group 3 : 1150). But the incidence of loco-regional lymphnodes (PSLN and SCLN) metastases was lower in the irradiated group 2 (050) compared to Group 1 (650) and Group 3 (850).Conclusion: Loco-regional lymphnodes irradiation after mastectomy for breast cancer with biopsy proven parasternal lymphnodes metastases did not increase DFS, but decrease the incidence of loco-regional recurrences.