Critical care has focused on recovery from acute organ failure and resuscitation. Neuromuscular abnormalities related to critical illness is not uncommon in critically ill patients, but they were relatively underestimated and unnoticed. Intensive care unit acquired weakness (ICUAW) leading to severe functional impairments in ICU survivors can be divided into two disease entities: critical illness polyneuropathy (CIP) and critical illness myopathy (CIM). Electrophysiologic study, muscle biopsy and physical examination are helpful to diagnose ICUAW. Several researches and reviews identified many risk factors including systemic inflammation, corticosteroids, hyperglycemia, and immobility. Additional research is needed to identify the pathogenesis of this disorder and to testify its preventive or therapeutic modalities.