The purpose of this study was to determine the clinical and electromyographical characteristics of the initial picture, and the subsequent course of the radiation-induced brachial plexopathy. The AA. studied 13 females affected by infiltrating carcinoma of the breast, who underwent a radical mastectomy with removal of the axillary cavity, followed by radiotherapy (total dose was 50 Gy per cycle). The symptom-free interval between the end of radiotherapy and the appearance of symptoms varied considerably (from one month to 15 years). The initial clinical picture presented pain (5 cases), paresthesia (6 cases) and motor deficit (8 cases). EMG examination showed a pluriradicular denervation in 10 cases (with a very frequent damage of the lower roots of the plexus) and a monoradicular denervation in 3 cases. In 6 cases it was possible to carry out a follow-up with repeated tests for 3-17 years after radiotherapy. The role of the EMG in the diagnosis and prognosis of this plexopathy is then discussed.