Persistent pulmonary hypertension of the newborn (PPHN) is a complex syndrome characterized by increased pulmonary vascular resistance (PVR) resulting in right-to-left shunting across the fetal channels. PPHN may be primary or secondary to a variety of conditions including intrapartum asphyxia, infection, pulmonary hypoplasia, and congenital heart disease. The incidence of PPHN is reported to be 0.43 - 6.8% / 1000 live births and the mortality related to PPHN is about 10 – 20 %.Sildenafil a relatively new drug is phosphodiesterase type 5 (PDE5) inhibitor that selectively reduces pulmonary vascular resistance (Michelakis et al., 2002). The dosage range generally used was 0.5-2mg/Kg/dose at 6 hourly intervals with dose titration based on response The present study was designed to evaluate the efficacy and safety of oral sildenafil in treatment of persistent pulmonary hypertension. This study was conducted on 30 neonates with PPHN admitted immediately or shortly after birth to the neonatal intensive care unit in Obstetrics and gynecology hospital at Cairo university hospitals.