Massive obstetric haemorrhage (MOH) is a leading cause of maternal morbidity and mortality world-wide. Using the Australian and New Zealand Massive Transfusion Registry, we performed a bi-national cohort study of MOH defined as bleeding at ≥20 weeks’ gestation or postpartum requiring ≥5 red blood cells (RBC) units within 4 h. Between 2008 and 2015, we identified 249 cases of MOH cases from 19 sites. Predominant causes of MOH were uterine atony (22%), placenta praevia (20%) and obstetric trauma (19%). Intensive care unit admission and/or hysterectomy occurred in 44% and 29% of cases, respectively. There were three deaths. Hypofibrinogenaemia (<2 g/l) occurred in 52% of cases in the first 24 h after massive transfusion commenced; of these cases, 74% received cryoprecipitate. Median values of other haemostatic tests were within accepted limits. Plasma, platelets or cryoprecipitate were transfused in 88%, 66% and 57% of cases, respectively. By multivariate regression, transfusion of ≥6 RBC units before the first cryoprecipitate (odds ratio [OR] 3·5, 95% CI: 1·7–7·2), placenta praevia (OR 7·2, 95% CI: 2·0–26·4) and emergency caesarean section (OR 4·9, 95% CI: 2·0–11·7) were independently associated with increased risk of hysterectomy. These findings confirm MOH as a major cause of maternal morbidity and mortality and indicate areas for practice improvement.