This study was aimed at evaluating the efficacy of ibuprofen in the prophylaxis of patent ductus arteriosus (PDA) in very preterm neonates and at detecting eventual side-effects. A total of 46 preterm neonates with gestational age under 31 weeks were randomly assigned at 2 h of life: 23 to the prophylaxis group and 23 to the control group. The prophylaxis group received intravenous treatment with ibuprofen lysine (10 mg/kg), followed by 5 mg/kg after 24 h and 48 h. No placebo was given to the control group. No PDA was demonstrated at 72 h of life in 20 of the 23 babies in the ibuprofen group (87%) nor in 7 of the 23 control neonates (30.4%). All neonates with PDA received treatment with indomethacin. One neonate in the prophylaxis group and three in the control group underwent surgical ligation. Prophylaxis with ibuprofen was not associated with any significant side-effect except for food intolerance.