Background: Treatment of multi-drug-resistant strains of pneumonia with common antibiotics in renal patients is ineffective and physicians are compelled to use Colistin for such cases. Objectives: This study was conducted to assess the mortality, length of stay, and renal damages in the treatment of multi-drugresistant pneumonia with Colistin among multiple trauma patients admitted to the emergency department and transferred to the ICU. Methods: This retrospective cohort study was conducted between 2011 and 2016. 102 multiple trauma (MT) patients with multidrug-resistant strains of hospital-acquired pneumonia (HAP) admitted to the emergency department then transferred to the ICU were assessed. All patients received Colistin according to their weight. Renal damage was evaluated according to the RIFLE criteria. The mortality and the length of stay were assessed. In order to statistically analyze the data, SPSS version 23 software was used to conduct t-test and chi-square test. Results: Out of 102 patients, 55 (54%) died and 50 (49.1%) developed acute renal failure; 64 cases had no hypertension. Patients according to the RIFLE index were assessed: Risk (11.01%), Injury (14%), Failure (18%), Loss (6%), and End-stage renal disease. The prevalence and prognosis of acute kidney injury in multiple trauma patients treated with Colistin were significantly correlated with drug dosage, body mass index, and use of corticosteroids (when assessed using relevant scoring systems, P < 0.05). Conclusions: The use of a scoring system in the intensive care unit, determining those patients requiring Colistin, and adjusting the dosage of this drug for treatment of MT patients with multi-drug resistant strains of HAP are vital. Creatinine levels must be carefully monitored.