This study was to assess the course and prognosis for acute kidney injury (AKI) in late onset sepsis in preterm newborns. It was to identify risk factors for death. The additional aim - to apply RIFLE criteria for classification the severity of AKI in newborns. A retrospective study performed in the Neonatology Clinic UJCM in Krakow between the years 2004-2009. 80 preterm newborns with LOS were divided into two groups: examined group – 39 patients with AKI, and control group – 41 without AKI. The results: AKI in the course of sepsis increased mortality The potential risk factors of death: hypotensia, oliguria, use of dopamine, furosemide, catecholamines, and exitstence of a pathogen other than Coagulase negative staphylococcus. The rise in CRP proved to be an independent factor diminishing risk of death. MOF accompanying sepsis appeared 10 times more often in the group with AKI. There were no important differences in comorbidities such as IVH, PDA and BPD between two groups. The mean time of assisted ventilation was longer in the group with AKI. Intrinsic renal failure was more frequent in the AKI group.The pRIFLE classification for severity of AKI is usually based on 2 criteria: serum creatinine changes (RIFLEGFR) and urinary output (RIFLEUo), which should be investigated separately for preterm newborns. Compared to other tests and markers of AKI the modification of RIFLEGFR (but not RIFLEUo) was an useful scale. The sensitivity of RIFLEGFR came to 75% and specificity 97%.