The aim of this study was to identify the nature of the nerve lesions found in patients with neurological complains and with lymphedema occurring after breast cancer treated by surgery and radiotherapy. Twelve patients treated in a specialised centre for lymphology had clinical and neurophysiological examinations. This study found 9 radiation-induced plexopathies, 1 neoplasic plexopathy, 2 carpal tunnel syndromes (one isolated), 1 cervical root disease and 1 normal examination. The radiation-induced plexopathy is characterised by a chronic neurogenic involvement and the presence of (motor and sensory) proximal persistent conduction blocks. This study demonstrated that it is essential to identify with electrodiagnosis the exact nature of the nerve lesion to determine the most appropriate and effective treatment.