An outbreak of Multi-Drug Resistance Pseudomonas aeruginosa (MDRP) infections occurred in intensive care unit (ICU) and emergency room (ER) between June and August 2007. Five patients who isolated MDRP in the outbreak of 2007 were all used bronchoscopes, thus, we suspected contamination of the bronchoscopes as the cause of outbreak. Although we did not detect MDRP from any bronchoscopes, the outbreak finally ended after all the bronchoscopes had been disinfected appropriately with the reexamination of washing process in 2008 and 2009. We retrospectively reviewed eleven patients who isolated MDRP in 2006 and 2007, and the fact was revealed that bronchoscopes were used in most patients in ICU and ER. Bronchoscopes were significantly used during 2006-2007 period, compared with 2008-2009 period in ICU and ER, and the case-control analysis among all Pseudomonas aeruginosa isolated patients identified that bronchoscopes [risk ratio (RR) 8.25, 95% confidence interval (CI) 1.328-51.26] was one of the most important risk factors for MDRP isolation. Duration from admission to MDRP isolation was significant longer in MDRP-isolated cases (19.82±12.77 d), compared with in non MDRP-isolated controls (11.76±11.69 d: p=0.0453). Our epidemiological analysis suggested the significant risk factors for an MDRP outbreak, and could contribute the estimation of the focus and prevention of future outbreaks.