Continuous electronic fetal monitoring (EFM) in labour is widely used and computerised interpretation has the potential to increase its utility. This trial aimed to find out whether or not the addition of decision support software to assist in the interpretation of the cardiotocograph (CTG) reduced the number of poor neonatal outcomes, and whether or not it was cost-effective. Two-arm individually randomised controlled trial. The allocations were computer generated using stratified block randomisation employing variable block sizes. The trial was not masked. Labour wards in England, Scotland and the Republic of Ireland. Women in labour having EFM, with a singleton or twin pregnancy, at ≥ 35 weeks' gestation. Decision support or no decision support. The primary outcomes were (1) a composite of poor neonatal outcome {intrapartum stillbirth or early neonatal death (excluding lethal congenital anomalies), or neonatal morbidity [defined as neonatal encephalopathy (NNE)], or admission to a neonatal unit within 48 hours for ≥ 48 hours (with evidence of feeding difficulties, respiratory illness or NNE when there was evidence of compromise at birth)}; and (2) developmental assessment at the age of 2 years in a subset of surviving children. Between 6 January 2010 and 31 August 2013, 47,062 women were randomised and 46,042 were included in the primary analysis (22,987 in the decision support group and 23,055 in the no decision support group). The short-term primary outcome event rate was higher than anticipated. There was no evidence of a difference in the incidence of poor neonatal outcome between the groups: 0.7% (n = 172) of babies in the decision support group compared with 0.7% (n = 171) of babies in the no decision support group [adjusted risk ratio 1.01, 95% confidence interval (CI) 0.82 to 1.25]. There was no evidence of a difference in the long-term primary outcome of the Parent Report of Children's Abilities-Revised with a mean score of 98.0 points [standard deviation (SD) 33.8 points] in the decision support group and 97.2 points (SD 33.4 points) in the no decision support group (mean difference 0.63 points, 95% CI -0.98 to 2.25 points). No evidence of a difference was found for health resource use and total costs. There was evidence that decision support did change practice (with increased fetal blood sampling and a lower rate of repeated alerts). Staff in the control group may learn from exposure to the decision support arm of the trial, resulting in improved outcomes in the control arm. This was identified in the planning stage and felt to be unlikely to have a significant effect on the results. As this was a pragmatic trial, the response to CTG alerts was left to the attending clinicians. This trial does not support the hypothesis that the use of computerised interpretation of the CTG in women who have EFM in labour improves the clinical outcomes for mothers or babies. There continues to be an urgent need to improve knowledge and training about the appropriate response to CTG abnormalities, including timely intervention. Current Controlled Trials ISRCTN98680152. This project was funded by the National Institute for Health Research (NIHR) HTA programme and will be published in full in Health Technology Assessment; Vol. 22, No. 9. See the NIHR Journals Library website for further project information. Sara Kenyon was part funded by the NIHR Collaboration for Leadership in Applied Health Research and Care West Midlands.