The study was performed to assess microorganisms and antibiotic susceptibility patterns during ten years in intensive care units of a University Hospital. Infection Control Committee has active, prospective surveillance in ICUs for thirteen years. Ten years data of ICUs was evaluated retrospectively from surveillance forms. Microorganisms and their antibiotic resistance were recorded according to the years. During ten years, gram negative microorganisms were the most frequent isolated microorganisms from clinical specimens. Acinetobacter baumannii (21.8%), Pseudomonas aerigunosa (16%), Escherichia coli (10.4%) and Klebsiella pneumoniae (8%) were the most common gram negative microorganisms. However, Staphylococcus aureus was the most prevalent gram positive microorganism, the incidence decreased from 18.6% to 4.8% during ten years. Also antibiotic susceptibility of microorganisms changed during ten years. Carbapenem resistance increased from 44% to 92% in A. baumannii and ciprofloxacin resistance increased in E. coli from 28% to 60% and in K. pneumoniae from 21% to 55% during ten years. However, methicilin resistance decreased in S. aureus from 96% to 54%. In conclusion, antibiotic resistance is growing problem in ICUs. Rationale antibiotic policies and infection control measures will prevent the development of resistance. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.