A colistin-glycopeptide combination (CGC) has been shown in vitro to be synergistic against multidrug-resistant Gram-negative bacteria (MDR GNB), especially Acinetobacter baumannii, and to prevent further resistance. However, clinical data are lacking. We carried out a retrospective multicenter study of patients hospitalized in intensive care units (ICUs) who received colistin for GNB infection over a 1-year period, to assess the rates of nephrotoxicity and 30-day mortality after treatment onset among patients treated with and without CGC for ≥48 h. Of the 184 patients treated with colistin, GNB infection was documented for 166. The main causative agents were MDR A. baumannii (59.6%), MDR Pseudomonas aeruginosa (18.7%), and carbapenem-resistant Klebsiella pneumoniae (14.5%); in 16.9% of patients, a Gram-positive bacterium (GPB) coinfection was documented. Overall, 68 patients (40.9%) received CGC. Comparison of patients treated with and without CGC showed significant differences for respiratory failure (39.7% versus 58.2%), ventilator-associated pneumonia (54.4% versus 71.4%), MDR A. baumannii infection (70.6% versus 52%), and GPB coinfection (41.2% versus 0%); there were no differences for nephrotoxicity (11.8% versus 13.3%) and 30-day mortality (33.8% versus 29.6%). Cox analysis performed on patients who survived for ≥5 days after treatment onset showed that the Charlson index (hazard ratio [HR], 1.26; 95% confidence interval [CI], 1.01 to 1.44; P = 0.001) and MDR A. baumannii infection (HR, 2.51; 95% CI, 1.23 to 5.12; P = 0.01) were independent predictors of 30-day mortality, whereas receiving CGC for ≥5 days was a protective factor (HR, 0.42; 95% CI, 0.19 to 0.93; P = 0.03). We found that CGC was not associated with higher nephrotoxicity and was a protective factor for mortality if administered for ≥5 days.