The aim of this study was to evaluate resistance rates to ciprofloxacin and levofloxacin of Pseudomonas aeruginosa (n=1917 strains) isolated at Laboratory of Microbiology at L. Sacco Teaching Hospital in Milan, Italy in the period between January 1998 and October 2002. Twenty-five percent of tested strains were isolated from sputum, 18% from bronchial lavage, 10% from urine, 9% from ear, 4.5% from blood and 26% from other materials. Ciprofloxacin-resistant strains were 121/ 411 (29%) in 1998, 158/ 526 (30%) in 1999, 136/ 400 (34%) in 2000, 129/390 (33%) in 2001 and 53/ 190 (28%) in 2002. Resistance rates for levofloxacin were 132/472 (28%) in 1999, 104/ 400 (26%) in 2000, 101/ 390 (26 %) in 2001 and 47/ 190 (25%) in 2002. Our data highlight overall stability in resistance to ciprofloxacin and levofloxacin with minor variations for ciprofloxacin. Moreover, in contrast with international worldwide studies, resistance rates to ciprofloxacin remained higher than those related to levofloxacin throughout the period studied.