A total of 674 clinical isolates of Pseudomonas aeruginosa were collected from 30 different hospitals located in 26 cities of Poland. These were 12 big regional hospitals, 7 large teaching hospitals, 4 specialised hospitals curing patients from the whole country, 6 small local hospitals and one regional paediatric hospital. The majority of strains were collected from patients hospitalised at ICUs (25.7%), surgical (21.7%), and internal medicine wards (9.9%). The isolates were recovered from different types of infections, mostly from respiratory tract infections (33.7%), wound infections (22.3%), and urinary tract infections (22.0%). All the isolates were subjected to antimicrobial susceptibility testing by MIC values evaluation. MICs of 13 different antibiotics (beta-lactams, aminoglycosides, chinolones) were determined by the agar dilution method. The general level of resistance of P.aeruginosa observed in the study was high, especially when compared to results of surveys obtained in other countries. Out of the antimicrobials used the highest activity in vitro was observed with meropenem, imipenem, piperacillin--tazobactam and ceftazidime. The high in vitro activity of ceftazidime was striking considering the long time of the use of this antibiotic in Polish hospitals. The highest levels of resistance were observed to some of the aminoglycosides. Populations of strains isolated in different wards or hospitals of different size were characterised by different susceptibility patterns.