The present case report describes how brachial plexopathy was evaluated in a patient who underwent radiation therapy for breast carcinoma after a latent interval of 17 years. A 63-year old woman presented with pain in her left shoulder, numbness and weaknesses in her left upper extremity, with a history of left mastectomy due to breast carcinoma and regional radiation exposure, diabetes mellitus type II, hypertension, high cholesterol levels, and obesity. Neurological examination revealed general weaknesses in her left arm, which was more prominent at the distal muscles, with an absence of deep tendon reflexes at the same extremity. Electromyography examination suggested injury at the posterior and medial cords of the left brachial plexus. The long duration of latency suggests that breast cancer patients who have undergone radiation therapy in may experience a life-long risk for brachial plexopathy.