Bilateral phrenic nerve paralysis is a rare potentially life-threatening condition which is usually due to trauma (including surgery) or neurologic disease. We present a patient with apparent rapid onset bilateral phrenic nerve paralysis whose primary symptom was severe positional (supine) dyspnea with profound supine oxygen desaturation. Nerve conduction study abnormalities of the phrenic nerves and some left brachial plexus nerves suggested a diagnosis of ALS. He was treated with supportive night time ventilatory assistance (BiPAP) and over 4 years his condition recovered essentially completely. In retrospect the most likely diagnosis was a rare brachial plexopathy referred to as neuralgic amyotrophy.