Background: Colistimethate sodium (CMS) treatment has increased over the last years, being acute kidney injury (AKI) its main drug-related adverse event. Therefore, this study aimed to evaluate the incidence and risk factors associated with AKI, as well as identifying the factors that determine renal function (RF) outcomes at six months after discharge. Materials and methods: This retrospective study included adult septic patients receiving intravenous CMS for at least 48 h (January 2007–December 2014). AKI was assessed using KDIGO criteria. The glomerular filtration rate (GFR) was estimated by the 4-variable MDRD equation. Logistic and linear models were performed to evaluate the risk factors for AKI and chronic kidney disease (CKD). Results: Among 126 patients treated with CMS; the incidence of AKI was 48.4%. Sepsis–severe sepsis (OR 8.07, P = 0.001), sepsis–septic shock (OR 42.9, P