Ecological surveys of high-antibiotic use areas in the hospital should be used to evaluate patterns and trends in order to optimise antibiotic consumption and minimise resistance. We conducted a retrospective cohort study with the aim to examine trends in antimicrobial consumption and bacterial susceptibility at the Geneva University Hospital and its adult ICUs between 1996 and 2000. The average annual consumption of antimicrobials was 400 d-defined doses (DDD)/1000 patient-d in the entire hospital, 462 in the surgical ICU and 683 in the medical ICU. In the medical ICU, we observed a steady decrease of intravenous antimicrobial use, whereas a 25% increase in the total antimicrobial consumption was noted in 1999 and 2000 for the entire hospital. The proportion of different bacterial species, resistance rates and antibiotic consumption rates differed between the entire hospital and the ICUs, with moderate variation between y. Possible relationships between antibiotic consumption and resistance rates, expressed as DDD and as number of resistant isolates per 1000 patient-d respectively, were calculated for of the most frequently isolated bacteria (total 71 correlations). Statistically significant positive correlations between antibiotic consumption and resistance were found in Escherichia coli for piperacillin, in Pseudomonas aeruginosa for piperacillin, cephalosporins and aminoglycosides, in Klebsiella spp. for cephalosporin, in coagulase-negative staphylococci for gentamicin and in Streptococcus pneumoniae for penicillin.