Simulation-based obstetric team training focuses on building a system that will anticipate errors, improve patient outcomes and the performance of clinical care teams. Simulation-based obstetric team training has been proposed as a tool to improve the overall outcome of obstetric health care. To assess the effects of simulation-based obstetric team training on patient outcomes, performance of obstetric care teams in practice and educational settings, and trainees' experience. The Cochrane Pregnancy and Childbirth Group's Trials Register, ClinicalTrials.gov and the WHO International Clinical Trials Registry Platform (ICTRP) were searched (14 April 2020), together with references checking and hand searching the available proceedings of 2 international conferences. We included randomised controlled trials (RCTs) (including cluster-randomised trials) comparing simulation-based obstetric team training with no, or other type of training. We used standard methodological procedures expected by Cochrane, to identify articles, assess methodological quality and extract data. Data from three cluster-randomised trials could be used to perform generic inverse variance meta-analyses. The meta-analyses were based on risk ratios (RRs) and mean differences (MDs) with 95% confidence intervals (CIs). We used the GRADE approach to rate the certainty of the evidence. We used Kirkpatrick's model of training evaluation to categorise the outcomes of interest; we chose Level 3 (behavioural change) and Level 4 (patient outcome) to categorise the primary outcomes. We included eight RCTs, six of which were cluster-randomised trials, involving more than 1000 training participants and more than 200,000 pregnancies/births. Four studies reported on outcome measures on Kirkpatrick level 4 (patient outcome), three studies on Kirkpatrick level 3 (performance in practice), two studies on Kitkpatrick level 2 (performance in educational settings), and none on Kirkpatrick level 1 (trainees' experience). The included studies were from Mexico, the Netherlands, the UK and the USA, all middle- and high-income countries. Kirkpatrick level 4 (patient outcome) Simulation-based obstetric team training may make little or no difference for composite outcomes of maternal and/or perinatal adverse events compared with no training (3 studies; n = 28,731, low-certainty evidence, data not pooled due to different composite outcome definitions). We are uncertain whether simulation-based obstetric team training affects maternal mortality compared with no training (2 studies; 79,246 women; very low-certainty evidence). However, it may reduce neonatal mortality (RR 0.70, 95% CI 0.48 to 1.01; 2 studies, 79,246 pregnancies/births, low-certainty evidence). Simulation-based obstetric team training may have little to no effect on low Apgar score compared with no training (RR 0.99, 95% 0.85 to 1.15; 2 studies; 115,171 infants; low-certainty evidence), but it probably reduces trauma after shoulder dystocia (RR 0.50, 95% CI 0.25 to 0.99; 1 study; moderate-certainty evidence) and probably slightly reduces the number of caesarean deliveries (RR 0.79, 95% CI 0.67 to 0.93; 1 study; n = 50,589; moderate-certainty evidence) Kirkpatrick level 3 (performance in practice) We found that simulation-based obstetric team training probably improves the performance of the obstetric teams in practice, compared with no training (3 studies; 2398 obstetric staff members, moderate-certainty evidence, data not pooled due to different outcome definitions). Simulation-based obstetric team training may help to improve team performance of obstetric teams, and it might contribute to improvement of specific maternal and perinatal outcomes, compared with no training. However, high-certainty evidence is lacking due to serious risk of bias and imprecision, and the effect cannot be generalised for all outcomes. Future studies investigating simulation-based obstetric team training compared to training courses with a different instructional design should carefully consider how and when to measure outcomes. Particular attention should be paid to effect measurement at the level of patient outcome, taking into consideration the low incidence of adverse maternal and perinatal events.