Introduction. Antimicrobial resistance has been identified as one of the major public health problems worldwide. To facilitate its control, bacterial resistance levels must be monitored permanently by effective surveillance systems.Objective. To describe the antimicrobial resistance patterns of Gram negative bacilli in Colombian hospitals over a 3-year period.Materials and methods. This descriptive study used the bacterial susceptibility profiles provided by 14 tertiary-care hospitals belonging to the Colombian Nosocomial Resistance Study Group. The hospitals were located in 7 major cities in Colombia, and provided records over the period January 2006 to December 2008. Using WHONET 5.4, the antimicrobial resistance patterns were described for the Enterobacteriaceae (Escherichia coli, Klebsiella pneumoniae and Enterobacter cloacae) and non-fermenters (Pseudomonas aeruginosa and Acinetobacter baumannii). Comparisons were made in the bacterial responses to selected antibiotics in samples from general wards and from adult intensive care units.Results. The antimicrobial resistance frequencies of several Enterobacteriaceae species showed a decreasing trend. In contrast, P. aeruginosa was demonstrated to be a multidrug-resistance organism with increasing resistance frequencies.Conclusions. These data emphasize the importance of surveillance programs in detecting presence of multidrug-resistant organisms. This information will aid the implementation of protocols aimed to strengthen the infection control strategies and antibiotic stewardship in each hospital.