OBJECTIVE To compare the efficacy and safety of oral versus intravenous ibuprofen for the pharmacological closure of patent ductus arteriosus (PDA) in less mature preterm infants. METHODS Prospective, randomised controlled study. METHODS Tertiary neonatal intensive care unit. METHODS The study enrolled 80 preterm infants with gestational age ≤28 weeks, birth weight <1000 g, postnatal age 48 to 96 h, and had echocardiographically confirmed significant PDA. Seventy extremely low birthweight (ELBW) preterm infants received either intravenous or oral ibuprofen randomly as an initial dose of 10 mg/kg, followed by 5 mg/kg at 24 and 48 h. METHODS The success rate and the safety of the drugs in ELBW preterm infants were the major outcomes. RESULTS PDA closure rate was significantly higher with oral ibuprofen (83.3% vs 61.7%) after the first course of the treatment (p=0.04). Although the primary closure rate was marginally higher in the oral ibuprofen group, the need for a second course of ibuprofen during the whole hospitalisation was similar between groups: 11 of 36 in oral versus 15 of 34 in intravenous groups (p=0.24) because of a higher reopening rate in the oral group. In addition to no increase in side effects with oral ibuprofen use, the need for postnatal steroid use for chronic lung disease was significantly lower in oral ibuprofen group (p=0.001). CONCLUSIONS Oral ibuprofen is as effective as intravenous ibuprofen for PDA closure even in ELBW infants.