The frequency of occurrence and antimicrobial susceptibility patterns of 3059 non-enteric Gram-negative bacilli (NGB), other than Pseudomonas aeruginosa and Acinetobacter spp., consecutively collected as part of the SENTRY Antimicrobial Surveillance Program (1997-2003) were reviewed. During this period, a total of 221,084 bacterial isolates were collected from several clinical specimens worldwide, including 25,305 (11.5%) NGB. Acinetobacter spp. and P. aeruginosa accounted for 82.7% of the NGB isolates and have been excluded from this analysis. The antimicrobial susceptibility results of 3509 strains from 13 species/genera have been analysed in this review. The isolates were tested by reference broth microdilution methods in three central laboratories using common reagents and procedures. More than 30 antimicrobial agents were tested and the results for the 18 most active compounds are reported here. Stenotrophomonas maltophilia (2076 strains; 59.2%) was the most frequently isolated pathogen in this group, followed by Aeromonas spp. (385 strain; 11.0%), Burkholderia cepacia (269 strains; 7.7%), Pseudomonas fluorescens/putida (253 strains; 7.2%) and Alcaligenes spp. (236 strains; 6.7%). All other species/genera accounted for less than 3% of the isolates analysed. The antimicrobial agents with the most consistent activity against the NGB evaluated in the present study were the newer fluoroquinolones gatifloxacin and levofloxacin with 84.1 and 84.9% susceptibility overall. Trimethoprim/sulphamethoxazole was active against 85.3% of the isolates tested, but showed reduced activity against P. fluorescens/putida (22.1% susceptibility). Antimicrobial susceptibility varied significantly between species/genera and the geographical regions evaluated. Thus, proper identification and quantitative susceptibility testing will be required for the treatment of NGB infections. Extensive worldwide surveillance programmes remain extremely important to guide empirical antimicrobial therapy for rarely isolated pathogens and also for pathogens that are not routinely tested due to the lack of standardised susceptibility testing methods.