Critical illness polyneuropathy (CIP) and critical illness myopathy (CIM) occur commonly in the patients who havebeen on mechanical ventilation for more than 1 week. Even in some patients diagnosed with CIP, an underlyingmyopathy may be the primary cause of the muscle weakness. The cormorbid status of CIP and CIM is called as criticalillness polyneuropathy and critical illness myopathy (CIPNM). We describe a 56-year-old man with acute quadriparesisand areflexia after systemic inflammatory response syndrome. The diagnosis of CIPNM is important to avoid unnecessaryinvestigations and unreasonably pessimistic prognosis. Electrophysiologic studies are essential for the diagnosis and forplanning further clinical management.