A clinical study was made of the occurrence of lymphoedema of the arm following radical mastectomy and modified radical mastectomy for curable breast cancer. The relation between this incidence and the occurrence of axillary node metastases and subsequent radiation to the axilla was examined. Both radical surgery and radiation increased the risk of postoperative arm lymphoedema. By changing the surgical approach towards less extensive operations this risk has been substantially reduced while radiation therapy still implies a high risk for persistent lymphoedema.