Nosocomial pneumonia caused by multidrug-resistant (MDR) Pseudomonas aeruginosa is becoming increasingly prevalent throughout the world. The use of polymyxins to treat these infections has greatly increased. We analysed 74 patients with nosocomial pneumonia caused by MDR P. aeruginosa who were treated with polymyxin B. A favourable outcome was observed in 35 patients (47.3%). A case-control study was performed to assess the variables associated with an unfavourable outcome. The presence of acute respiratory distress syndrome (odds ratio (OR)=11.29, 95% confidence interval (CI) 2.64-48.22; P=0.001) and septic shock (OR=4.81, 95% CI 1.42-16.25; P=0.01) were independently associated with an unfavourable outcome in patients with nosocomial pneumonia due to MDR P. aeruginosa. Our study demonstrated that polymyxin B is a reliable antimicrobial drug, but only as salvage therapy, for nosocomial pneumonia caused by MDR P. aeruginosa.