We studied five patients in the intensive care unit (ICU) with acute polyneuropathy. All had previously presented severe infectious processes, accompanied by diverse organ failure accompanied by the Adult Respiratory Distress Syndrome (ARDS) in all cases. Two patients died and the three survivors suffered severe motor deficiencies. Electromyographic studies revealed axonal damage which predominantly affected motor neurons. Cerebrospinal fluid was normal in all the patients except one, who showed a moderate increase of lymphocytes. The common causes of polyneuropathy were excluded, but in all cases a nutritional disorder was detected, based on laboratory values of proteins, serum albumin and transferrin. We conclude that polyneuropathy is relatively frequent among critically ill patients and must be closely monitored because of diagnostic difficulties and the repercussions on the progress of these patients. In spite of uncertainties about its cause, it appears to be related to severe infectious processes, ARDS, and nutritional disorders.