BACKGROUND: Improving maternal health by reducing maternal mortality constitutes the fifth Millennium Development Goal and represents a key public health challenge in the United Republic of Tanzania. In response to the need to evaluate and monitor safe motherhood interventions, this study aims at assessing the coverage of obstetric care according to the Unmet Obstetric Need (UON) concept by obtaining information on indications for, and outcomes of, major obstetric interventions. Furthermore, we explore whether this concept can be operationalized at district level. METHODS: A two year study using the Unmet Obstetric Need concept was carried out in three districts in Tanga Region, Tanzania. Data was collected prospectively at all four hospitals in the region for every woman undergoing a major obstetric intervention, including indication and outcome. The concept was adapted to address differentials in access to emergency obstetric care between districts and between rural and urban areas. Based upon literature and expert consensus, a threshold of 2% of all deliveries was used to define the expected minimum requirement of major obstetric interventions performed for absolute maternal indications. RESULTS: Protocols covering 1,260 complicated deliveries were analysed. The percentage of major obstetric interventions carried out in response to an absolute maternal indication was only 71%; most major obstetric interventions (97%) were caesarean sections. The most frequent indication was cephalo-pelvic-disproportion (51%). The proportion of major obstetric interventions for absolute maternal indications performed amongst women living in urban areas was 1.8% of all deliveries, while in rural areas it was only 0.7%. The high proportion (8.3%) of negative maternal outcomes in terms of morbidity and mortality, as well as the high perinatal mortality of 9.1% (still birth 6.9%, dying within 24 hours 1.7%, dying after 24 hours 0.5%) raise concern about the quality of care being provided. CONCLUSION: Based on the 2% threshold, Tanga Region - with an overall level of major obstetric interventions for absolute maternal indications of 1% and a caesarean section rate of 1.4% - has significant unmet obstetric need with a considerable rural-urban disparity. The UON concept was found to be a suitable tool for evaluating and monitoring the coverage of obstetric care at district level.