Objective: To investigate whether simulation-based obstetric team training in a simulation centre improves patient outcome. Design: Multicentre, open, cluster randomised controlled trial. Setting: Obstetric units in the Netherlands. Population: Women with a singleton pregnancy beyond 24 weeks of gestation. Methods: Random allocation of obstetric units to a 1-day, multi-professional, simulation-based team training focusing on crew resource management (CRM) in a simulation centre or to no such team training. Intention-to-treat analyses were performed at the cluster level, including a measurement 1 year prior to the intervention. Main outcome measures: Primary outcome was a composite outcome of obstetric complications during the first year post-intervention, including low Apgar score, severe postpartum haemorrhage, trauma due to shoulder dystocia, eclampsia and hypoxic-ischaemic encephalopathy. Maternal and perinatal mortality were also registered. Results: Each study group included 12 units with a median unit size of 1224 women, combining for a total of 28 657 women. In total, 471 medical professionals received the training course. The composite outcome of obstetric complications did not differ between study groups [odds ratio (OR) 1.0, 95% confidence interval (CI) 0.80–1.3]. Team training reduced trauma due to shoulder dystocia (OR 0.50, 95% CI 0.25–0.99) and increased invasive treatment for severe postpartum haemorrhage (OR 2.2, 95% CI 1.2–3.9) compared with no intervention. Other outcomes did not differ between study groups. Conclusion: A 1-day, off-site, simulation-based team training, focusing on teamwork skills, did not reduce a composite of obstetric complications. Tweetable abstract: 1-day, off-site, simulation-based team training did not reduce a composite of obstetric complications.