Objective: To describe the clinical response and overall mortality of Colistin in infections by Pseudomonas XDR and Acinetobacter XDR at the Hospital Nacional Arzobispo Loayza in Lima, Peru. Methods: Observational, descriptive, retrospective study. Records of all patients > 18 years old, from June 2014 to June 2016, who had infection by Pseudomonas XDR or Acinetobacter XDR confirmed by culture, and who received colistin, were included. A univariate analysis of the general characteristics of the patients was performed; a bivariate analysis with a Chi2, t-student or ANOVA test as appropriate, and the factors associated with mortality were also determined. Results: 56 patient records were included; the median age was 46,5 [31,5 to 63,5]. The Culture was positive for Pseudomonas XDR in 48,2% and for Acinetobacter XDR in 51,8%. The favorable clinical response was 85,7% at 15 days and 78,6% at 30 days. In-hospital mortality at 30 days was 21,4%, ICU mortality was 30,8% and nephrotoxicity was 5,4%. Conclusions: Colistin combined with another antimicrobial had a favorable clinical response in infection with Pseudomonas XDR and Acinetobacter XDR.