Critical illness polyneuro-and/or myopathy (CIP/CIM) is an important and frequent complication in the intensive care unit (ICU), causing delayed weaning from mechanical ventilation. It may increase ICU stay and mortality.To examine the ability of any intervention to prevent the occurrence of CIP/CIM.We searched the Cochrane Neuromuscular Disease Group Trials Register (October 2007), MEDLINE (January 1950 to April 2008), EMBASE (January 1980 to October 2007), checked bibliographies and contacted trial authors and experts in the field.All randomised controlled trials (RCTs), examining the effect of any intervention on the incidence of CIP/CIM in adult medical or surgical ICU patients. The primary outcome measure was the incidence of CIP/CIM after at least seven days in ICU, based on electrophysiological or clinical examination.Two authors independently extracted the data.Three out of nine identified trials, provided data on our primary outcome measure. Two trials examined the effects of intensive insulin therapy versus conventional insulin therapy. Eight hundred and twenty-five out of 2748 patients randomised, were included in the analysis. The incidence of CIP/CIM was significantly reduced with intensive insulin therapy in the population screened for CIP/CIM (relative risk (RR) 0.65, 95% confidence interval (CI) 0.55 to 0.78) and in the total population randomised (RR 0.60, 95% CI 0.49 to 0.74). Duration of mechanical ventilation, duration of ICU stay and 180-day mortality but not 30-day mortality, were significantly reduced with intensive insulin therapy, in both the total and the screened population. Intensive insulin therapy significantly increased hypoglycaemic events and recurrent hypoglycaemia. Death within 24 hours of the hypoglycaemic event was not different between groups. The third trial examined the effects of corticosteroids versus placebo in 180 patients with prolonged acute respiratory distress syndrome. No significant effect of corticosteroids on CIP/CIM was found (RR 1.09, 95% CI 0.53 to 2.26). No effect on 180-day mortality, new serious infections and glycaemia at day seven was found. A trend towards fewer episodes of pneumonia and reduction of new events of shock was shown.Substantial evidence shows that intensive insulin therapy reduces the incidence of CIP/CIM, the duration of mechanical ventilation, duration of ICU stay and 180-day mortality. There was a significant associated increase in hypoglycaemia. Further research needs to identify the clinical impact of this and strategies need to be developed to reduce the risk of hypoglycaemia. Limited evidence shows no significant effect of corticosteroids on the incidence of CIP/CIM, or on any of the other secondary outcome measures, except for a significant reduction of new episodes of shock. Strict diagnostic criteria for the purpose of research should be defined. Other interventions should be investigated in randomised controlled trials.