Introduction: Acute renal failure (ARF) is a common problem among the admitted neonates in Intensive Care Units. In most of the patients, ARF accompanies with a predisposing factor such as sepsis, heart failure, perinatal asphyxia or prematurity. Due to the relatively high prevalence of ARF in neonates, the present study emphasizes on the fact that misdiagnosis and under treatment of ARF can lead to adverse complications. So, our objective is to find the frequency and etiology of renal failure among the admitted newborns in a NICU.Materials and Methods: In this study, the profiles of 2400 admitted newborns in the NICU of Bahman 22nd Hospital of Mashhad over a period of 5 years were reviewed. There were 50 newborns with the inclusion criteria of renal failure. Patients’ serum creatinin and urine volumes were measured and compared with a standard table. Finally, the data was analyzed by SPSS, setting a significance level of P£0.05.Results: The prevalence rate of ARF was found to be 2.1% with a rate of 2.3% among the male neonates and that of 1.8% among the females which was not significantly different (P=0.093). Concerning the type of renal failure, 18 neonates (36%) were diagnosed as renal ARF, 31 neonates (62%) as pre-renal ARF and 1 neonate (2%) as post-renal ARF. In this study, the most common causes of ARF were dehydration (28%), respiratory distress syndrome (18%), Icterous and poor feeding (16%), asphyxia (16%) and Infections (14%), respectively.Conclusion: Pre-renal factors, especially dehydration and poor feeding are the most common causes of acute renal failure in newborns.