The influence of postoperative radiation therapy on development of late arm lymphedema and shoulder joint disability following mastectomy was evaluated from a series of 57 women with operable carcinoma of the breast. The patients were divided into three groups. Common for all three groups was mastectomy and partial axillary dissection. In addition one group received postoperative irradiation plus systemic therapy and another group systemic therapy alone. The incidence of late arm lymphedema/impaired shoulder mobility was 11%/4% in the group of patients undergoing surgery alone, 46%/38% in the group of patients receiving adjuvant irradiation and 6%/12% in the group of patients receiving adjuvant systemic therapy. It is concluded that adjuvant irradiation to the axilla in patients with metastatic lymph nodes highly increases the risk of late physical sequelae following modified radical mastectomy. Adjuvant systemic therapy can be administered to high risk patients without increasing the risk of late arm lymphedema and shoulder disability.