This study analysed the time-trends for bacteria associated with nosocomial lower respiratory tract infections (LRTIs), bloodstream infections (BSIs) and urinary tract infections (UTIs) that were reported to the German Nosocomial Infection Surveillance System for intensive care units (ICUs). Data concerning 19 822 nosocomial infections were submitted by 139 ICUs between 2000 and 2005. There was a significant increase in the proportion of Gram-negative bacteria causing LRTIs (from 63.9% to 68.4%) and UTIs (from 65.3% to 68.6%). The proportion of BSIs caused by Gram-negative bacteria declined significantly, from 36.4% to 22.7%. The frequency of methicillin-resistant Staphylococcus aureus among all S. aureus isolates increased from 19.8% to 37.2%.