Multi-resistant bacterial strains are increasingly prevalent in hospital environments. Bacterial resistance is an important problem, especially for practitioners in intensive care units (ICUs) because of the selective pressure on the prevalent bacteria in these environments. The MYSTIC (Meropenem Yearly Susceptibility Test Information Collection) study has been monitoring the performance of carbapenems and other antibiotics in different hospitals for at least 3 years. The in vitro activities of meropenem, imipenem, ceftazidime, cefepime, cefotaxime, ciprofloxacin, piperacilin/tazobactam, gentamicin, and tobramycin were compared against 452 recent clinical aerobic isolates. The isolates consisted of 19 species of Gram-negative bacteria (n=290) including K. pneumoniae (n=49), E. coli (n=48), A. baumannii (n=47), Enterobacter spp. (n=41), and P. aeruginosa (n=33) and 9 species of Gram-positive bacteria (n=162) including Staphylococcus aureus (n=63), Enterococcus faecalis (n=22), Streptococcus pneumoniae (n=22) and coagulase negative Staphylococci (n=21). All isolates were collected from ICU patients. Minimal inhibitory concentrations (MICs) were determined by Etest methodology, using standardized and controlled procedures. Meropenem and imipenem showed the lowest MIC(90) for all species tested. Gram-negative isolates showed the following overall resistance percentages to the other 7 drugs: tobramycin (43.1%), cefotaxime (38.6%), gentamicin (34.1%), ceftazidime (31.7%), ciprofloxacin (25.5%), piperacillin/tazobactam (26.9%), and cefepime (18.6%). Carbapenems were the most active drugs overall and only P. aeruginosa presented some degree of resistance (18.2%). We also evaluated the production of extended spectrum beta-lactamase (ESBL) among all Enterobacteriaceae members (n=176) by Etest/ESBL strip. ESBL production was detected in 51 strains (29.0%). Among them, Klebsiella pneumoniae was the most prevalent at 59.2%, followed by Enterobacter spp. (19.5%) and E. coli (14.6%). The high level of resistance against several antimicrobials and the alarming rate of ESBL production may restrict therapeutic choice to the carbapenems in this selected group of patients.