Objective: To explore the efficacy and risks of oral paracetamol in later (>2 weeks old) treatment of patent ductus arteriosus (PDA). Study design: A multicentre double-blind placebo-controlled randomised pilot trial in three neonatal intensive care units in Australia. Infants born <33 weeks with haemodynamically significant PDA were treated with a 5-day course of oral paracetamol or placebo. Cardiac ultrasounds were used to document haemodynamic parameters. The primary outcome analysed was ductal closure by 48 h after treatment completion. Secondary outcomes included reduction in ductal diameter >25% and safety. Results: Fifty-five infants were enrolled, of whom 27 received paracetamol and 28 placebo. Eighty percent had received previous non-steroidal anti-inflammatory drug. Mean postnatal age was 25 days. Four of the 27 ducts treated with paracetamol closed vs. 0/28 treated with placebo (p = 0.05). An additional 13/27 given paracetamol vs. 7/28 given placebo showed significant constriction (p = 0.008). No adverse effects were observed. Conclusions: There was some evidence of increased closure with oral paracetamol at postnatal age >2 weeks; however, the overall efficacy was not high.