We analysed the AB usage of 70 German ICUs in the year 2011. The data were collected in a standardized way within the SARI (Surveillance of Antimicrobial Use and Antimicrobial Resistance in ICUs) system. AB use densities (AD) were calculated as daily defined doses (DDD) per 1000 patient days (pd) for all systemically applied substances. We performed a stepwise forward multivariable analysis for the total AB use as binary outcome (total AD <= or > 75. percentile). The following variables were included: hospital type (university, teaching, other), hospital size (<= or > 600 beds), ward type (interdisciplinary, surgical, medical ICU), ward size (<= or > 12 beds), number of used AB substances, number of used AB groups, ADs of AB treatment groups and fractions of most used AB groups.