Background: Perinatal (mortality) audit can be considered to be a way to improve the careprocess for all pregnant women and their newborns by creating an opportunity to learn from unwanted events in the care process. In unit-based perinatal audit, the caregivers involved in cases that result in mortality are usually part of the audit group. This makes such an audit a delicate matter. Methods: The purpose of this study was to implement unit-based perinatal mortality audit in all 15 perinatal cooperation units in the northern region of the Netherlands between September 2007 and March 2010. These units consist of hospital-based and independent community-based perinatal caregivers. The implementation strategy encompassed an information plan, an organization plan, and a training plan. The main outcomes are the number of participating perinatal cooperation units at the end of the project, the identified substandard factors (SSF), the actions to improve care, and the opinions of the participants. Results: The perinatal mortality audit was implemented in all 15 perinatal cooperation units. 677 different caregivers analyzed 112 cases of perinatal mortality and identified 163 substandard factors. In 31% of cases the guidelines were not followed and in 23% care was not according to normal practice. In 28% of cases, the documentation was not in order, while in 13% of cases the communication between caregivers was insufficient. 442 actions to improve care were reported for 'external cooperation' (15%), 'internal cooperation' (17%), 'practice organization' (26%), 'training and education' (10%), and 'medical performance' (27%). Valued aspects of the audit meetings were: the multidisciplinary character (13%), the collective and non-judgmental search for substandard factors (21%), the perception of safety (13%), the motivation to reflect on one's own professional performance (5%), and the inherent postgraduate education (10%). Conclusion: Following our implementation strategy, the perinatal mortality audit has been successfully ...