OBJECTIVE To assess the availability of obstetric institutions, the risk of unplanned delivery outside an institution and maternal morbidity in a national setting in which the number of institutions declined from 95 to 51 during 30 years. DESIGN Retrospective population-based, three cohorts and two cross-sectional analyses. SETTING Census data, Statistics Norway. The Medical Birth Registry of Norway from 1979 to 2009. POPULATION Women (15-49 years), 2000 (n = 1,050,269) and 2010 (n = 1,127,665). Women who delivered during the period 1979-2009 (n = 1,807,714). METHODS Geographic Information Systems software for travel zone calculations. Cross-table and multiple logistic regression analysis of change over time and regional differences. World Health Organization Emergency Obstetric and Newborn Care (EmOC) indicators. MAIN OUTCOME MEASURES Proportion of women living outside the 1-hour travel zone to obstetric institutions. Risk of unplanned delivery outside obstetric institutions. Maternal morbidity. RESULTS The proportion of women living outside the 1-hour zone for all obstetric institutions increased from 7.9% to 8.8% from 2000 to 2010 (relative risk, 1.1; 95% confidence interval, 1.11-1.12), and for emergency obstetric care from 11.0% to 12.1% (relative risk, 1.1; 95% confidence interval, 1.09-1.11). The risk of unplanned delivery outside institutions increased from 0.4% in 1979-83 to 0.7% in 2004-09 (adjusted odds ratio, 2.0; 95% confidence interval, 1.9-2.2). Maternal morbidity increased from 1.7% in 2000 to 2.2% in 2009 (adjusted odds ratio, 1.4; 95% confidence interval, 1.2-1.5) and the regional differences increased. CONCLUSIONS The availability of and access to obstetric institutions was reduced and we did not observe the expected decrease in maternal morbidity following the centralisation.