Objective: To determine the population-based rates of severe maternal morbidity during childbirth hospitalisation and associated characteristics in the Republic of Ireland and to directly compare incidence rates with Australia.Study design: Retrospective cohort study of 330,955 childbirth hospitalisations between 2005 and 2009. Using validated diagnostic criteria from Australia, we examined hospital discharge records (ICD-10-AM) to identify likely cases of severe maternal morbidity. We derived overall and category-specific morbidity incidence rates and examined five-year trends. Unadjusted relative risks were computed to assess sociodemographic and obstetric factors associated with morbidity status.Results: The severe maternal morbidity five-year incidence rate was 1.34 per 100 deliveries. Between 2005 and 2009, the overall rate of severe morbidity significantly increased from 1.31 to 1.55 cases per 100 deliveries (test for trend p-value <0.001). Similar to Australia, the most frequently diagnosed severe morbidity indicators in Ireland were blood transfusion (112.6 per 10,000 deliveries), evacuation of haematoma (7.2 per 10,000 deliveries) and dilation and curettage with general anaesthesia (3.9 per 10,000 deliveries). In the Irish cohort, the risk of severe morbidity was more than three-fold (RR 3.48; 95% CI: 3.06-3.95) among women carrying multiple gestations and more than four-fold (RR 4.37; 95% CI: 3.66-5.22) among women with a stillbirth. Further, severe morbidity risk was 2.62 times higher among women with a pre-existing medical condition (RR 2.62; CI 2.03-3.37).Conclusion: Our use of low-cost administrative data to identify severe maternal morbidity contributes to a growing body of international initiatives to inform preventive efforts. The ability to directly compare morbidity rates is advantageous, underscoring the need for a uniform definition of severe morbidity to promote accurate and reliable international comparisons. (C) 2012 Elsevier Ireland Ltd. All rights reserved.