Hospital-acquired pneumonia is the most frequent cause of mortality among nosocomial infections. The aim of this study was to determine the prevalence of hospital-acquired pneumonia in Trakya University Hospital as well as its causative agents, resistance patterns and change of these during ten years. The microbiology data collected from nosocomial pneumonia patients hospitalized between October 2003 and September 2004 were evaluated retrospectively and compared with former related data. Nosocomial pneumonia has increased to be the most frequent infection with 1.21% up to former third rank with 0.6% ratio. The most frequent agent was Acinetobacter; the frequency of Acinetobacter spp. has increased up to 44.5% from 38.2%. The second most frequent agent was Pseudomonas spp. in both studies. The most effective antibiotic on Acinetobacter was imipenem, but susceptibility to imipenem has decreased from 100% to 35%. In conclusion, hospital-acquired pneumonia is the most important cause of nosocomial infection in the author's hospital and antimicrobial resistance has increased considerably in the course of time.