Acquired neuromuscular weakness due to critical illness polyneuropathy and myopathy (CIPNM) frequently develops in patients hospitalized in the intensive care unit for more than 1 week. CIPNM may present with muscle weakness and failure to wean from mechanical ventilation, but is discovered more often and earlier by electrophysiological examination. In this review, the incidence, clinical and electrophysiological features, differential diagnosis and prognosis of CIPNM will be described. Risk factors for CIPNM are sepsis or systemic inflammatory response syndrome and the severity of multi-organ failure. Presence of CIPNM is associated with higher mortality rate, prolonged duration of mechanical ventilation and prolonged rehabilitation. The majority of survivors with CIPNM have persistent functional disabilities and a reduced quality of life. There is need for new therapeutic strategies to prevent or minimize CIPNM in critically ill patients.