Background: There are concerns about ethnic disparity in outcome of obstetric health care in high-income countries. Our aim was to assess these differences in a large cohort of women having experienced severe acute maternal morbidity (SAMM) during pregnancy, delivery and puerperium. Methods: All women experiencing SAMM were prospectively collected in a nationwide population-based design from August 2004 to August 2006. Women delivering in the same period served as reference cohort. Population-based risks were calculated by ethnicity and by type of morbidity. Additionally, non-Western and Western women having experienced SAMM were compared in multivariable logistic regression analysis. Results: All 98 Dutch maternity units participated. There were 371 021 deliveries during the study period. A total of 2506 women with SAMM were included, 21.1% of whom were non-Western immigrants. Non-Western immigrants showed a 1.3-fold [95% confidence interval (CI) 1.2–1.5] increased risk to develop SAMM. Large differences were observed among different ethnic minority groups, ranging from a non-increased risk for Moroccan and Turkish women to a 3.5-fold (95% CI 2.8–4.3) increased risk for sub-Saharan African women. Low socio-economic status, unemployment, single household, high parity and prior caesarean were independent explanatory factors for SAMM, although they did not fully explain the differences. Immigration-related characteristics differed by ethnic background. Conclusions: Non-Western immigrants have an increased risk of developing SAMM as compared to Western women. Risks varied largely by ethnic origin. Immigration-related characteristics might partly explain the increased risk. The results suggest that there are opportunities for quality improvement by targeting specific disadvantaged groups.