Neuralgic amyotrophy is characterized by acute onset of arm pain, followed after a variable interval by flaccid paralysis in the distribution of the brachial plexus on one or sometimes both sides. Electromyography reveals findings suggestive of an axonal degeneration process affecting various portions of the brachial plexus or individual nerves emanating from it, sometimes difficult to localize to discrete cords, trunks, or nerves. Diagnosis is established by excluding other causes, including compression and vasculitides. Prognosis for recovery is excellent.