We investigated whether large head circumference (HC) combined with persistent occiput posterior (OP) position is associated with higher rates of interventional delivery and obstetric and neonatal complications than OP alone or large HC alone. Term singleton deliveries in our centres from 1/2010-12/2014, delivered in vertex occiput anterior (n=41,038) or OP position (n=1740), were included. We compared delivery modes and rates of maternal and neonatal complications in OA vs. OP deliveries when HC≥90th centile; we further compared outcomes in only those delivered in persistent OP position, having HC≥90th centile vs. HC<90th centile. Persistent OP position combined with HC≥90th centile was associated with higher rates of vacuum and unplanned CS compared to those with HC<90th centile in OP position (20.1 vs. 17.2% [OR 1.53, 95% CI 0.99-2.36] and 23.4 vs. 9.2% [OR 3.326, 95% CI 2.17-5.11], respectively) or in OA position with HC≥90th (20.1% vs. 12.7% [OR 2.09, 95% CI 1.38-3.19] and 23.4% vs.12.5% [OR 2.48, 95% CI 1.66-3.7], respectively). Rates of prolonged second stage, failed vacuum extraction, and NICU admission were also increased over and above those in either OA with HC≥90th centile, or OP position with HC<90th centile. Multinomial regression modelling of delivery mode (NVD as reference group) showed that OP increased the risk of interventional delivery three-fold and HC≥90th centile further doubled the risk of vacuum delivery in primiparae and tripled it in multiparae. Large HC combined with OP position is associated with higher rates of interventional delivery and prolonged second stage of labour than those observed in OP delivery when HC <90th centile, as well as HC≥90th centile delivered in OA position. HC measurement might be included with other measures to assess women in labour, as it is associated with maternal and fetal outcomes in OP deliveries.