Brachial plexopathy is the most common complication of therapeutic irradiation affecting the peripheral nervous system. Patients treated for breast carcinoma are most often affected; radiation brachial plexopathy is a significant source of morbidity. Lumbosacral plexopathy is also an increasingly recognized complication of radiation therapy for a number of neoplasms. Newer radiation techniques, such as stereotactic body irradiation and intensity-modulated radiotherapy, also carry a risk of plexus injury. It is important for neurologists to diagnose radiation-induced plexopathies early and to differentiate them from plexus metastases or other causes of plexopathy. Dr. Dropcho of the Indiana University Medical Center discusses the clinical presentations, diagnostic issues, and management of patients with radiation plexopathies.