Background Critically ill patients may develop muscle weakness or paralysis during the course of sepsis and multiple-organ failure. We studied peripheral nerve and muscle disorders (NMD) in comatose patients. Methods Comatose patients who developed paralysis associated with absent deep-tendon reflexes had electroneuromyography (ENMG) and muscle-nerve biopsy specimens taken. Onset and duration of sepsis, multiple-organ dysfunction and failure, biochemical alterations, and drugs potentially interfering with nerve-muscle function were recorded. Findings 24 patients became quadriparetic or quadriplegic; muscle changes were found in 23. Axonal neuropathy was found in eight of 22 patients examined. All patients had prolonged sepsis and multiple-organ dysfunction, but only 14 had multiple-organ failure. Drugs such as steroids, neuromuscular-blocking agents, and aminoglycosides were not responsible for paresis, and the part played by hyperglycaemia and hypoalbuminaemia is uncertain. Attending physicians predicted a fatal outcome in all cases, although six of seven survivors fully recovered within 115-210 days from the onset of paralysis. Interpretation Comatose patients may become completely paralysed because of NMD. The diagnosis is important to avoid unnecessary investigations and unreasonably pessimistic prognosis. ENMG is essential for the diagnosis and for planning further clinical management. Biopsy needs to be done only when it is necessary to properly classify NMD.