Nosocomial infections caused by multidrug-resistant (MDR) microorganisms are a common problem around the world, especially in Intensive Care Units. The aim of this study was to investigate the efficacy and safety of colistin therapy in paediatric patients with severe nosocomial infections caused by MDR Gram-negative bacteria. There were 87 episodes in 79 paediatric Intensive Care Unit patients in five different hospitals; each patient was treated intravenously with colistin and evaluated. Of the 79 patients, 54.4% were male and the median age was 30 months. The most commonly isolated microorganism was Acinetobacter baumannii, the most common isolation site was tracheal aspirate fluid and the most common type of infection was ventilator-associated pneumonia. The mean colistin dose in patients without renal failure was 5.4 +/- 0.6 mg/kg/day, the mean therapy duration was 17.2 +/- 8.4 days and the favourable outcome rate was 83.9%. Serious side effects were seen in four patient episodes (4.6%) during therapy; two patients suffered renal failure and the others had convulsive seizures. Other patients tolerated the drug well. The infection-related mortality rate was 11.5% and the probability of death within the first 9 days of treatment was 10 times higher than after the first 9 days. In conclusion, this study suggests that colistin is effective in the treatment of severe nosocomial infections caused by MDR Gram-negative bacteria and is generally well tolerated by patients, even after relatively long-term use. (C) 2012 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.