Liveborn infants delivered before 37 week of postmenstrual age or less than 2,500g of birth weight are defined as premature infants. Recently, the unprecedented progress in neonatal practice has achieved remarkable improvements in the survival of extremely premature infants. However, immature organ function and the complication of therapy still contribute to the high mortality and morbidity from a spectrum of disease especially in extremely premature, low birth weight infants; respiratory distress syndrome, chronic lung disease, necrotizing enterocolitis, intraventricular hemorrhage, nosocomial infection, and prolonged hospitalization consist of the spectrum of disease in premature infants. To achieve further progress in neonatal-perinatal practice, randomized clinical trials should be employed not just to test the effectiveness of new therapies but also to evaluate competing strategies toward evidence-based, better clinical practic