Weakness is a common, though sometimes vague, presenting symptom in the ED. Neuromuscular (NM) weakness can have various causes, ranging from common and relatively easy to diagnose conditions (such as strokes and trauma) to less common and more difficult to diagnose ones (such as vascular pathologies, infections, autoimmune diseases, and neoplasms). This post focuses on how to localize weakness to differentiate types of NM weakness and presents classic cases of diffuse weakness caused by three diseases.