Multidrug-resistant (MDR) bacterial infections are increasing in Taiwan hospitals, prompting the common use of colistin. In this study, the safety and efficacy of intravenous (i.v.) colistin was assessed. The medical records of patients receiving colistin for treatment of MDR Gram-negative bacterial infections between January 2006 and September 2008 at a Taiwan medical centre were reviewed retrospectively. Demographics, clinical presentation, causative organism, adverse events and outcomes were recorded. Of the 115 patient records analysed, 74 patients (64%) were treated in the Intensive Care Unit. Common underlying diseases were hypertension (49%), chronic pulmonary disease (46%), chronic kidney disease (33%) and malignancy (31%). Lower respiratory tract infections were most common (71%), followed by primary bloodstream infections (12%), urinary tract infections (8.7%) and others (7.8%). Successful treatment with i.v. colistin against MDR Gram-negative bacterial infections occurred in 59 patients (51%). Multivariate analysis showed that a higher Acute Physiology and Chronic Health Evaluation (APACHE) II score (odds ratio=1.14; 95% confidence interval 1.02-1.28; P=0.02) was independently associated with a poor clinical response. Overall, 12 (14%) of 84 patients presented nephrotoxicity and 4 patients (3.5%) had neurotoxicity. In conclusion, colistin is an effective antimicrobial agent for severe infections caused by MDR Gram-negative bacteria. Clinical outcomes are associated with the severity of infection and underlying diseases. Compared with previous reports, this study showed a lower incidence of nephrotoxicity and neurotoxicity.