Comparing the relative effectiveness of interventions on specific outcomes across trials can be problematic due to differences in the choice and definitions of outcome measures used by researchers. We sought to identify a minimum set of outcome measures for evaluating models of maternity care from the perspective of key stakeholders.A 3-round, electronic Delphi survey design was used. Setting was multinational, comprising a range of key stakeholders. Participants consisted of a single heterogeneous panel of maternity service users, midwives, obstetricians, pediatricians/neonatologists, family physicians/general practitioners, policy-makers, service practitioners, and researchers of maternity care. Members of the panel self-assessed their expertise in evaluating models of maternity care.A total of 320 people from 28 countries expressed willingness to take part in this survey. Round 1 was completed by 218 (68.1%) participants, of whom 173 (79.4%) completed round 2 and 152 (87.9%) of these completed round 3. Fifty outcomes were identified, with both a mean value greater than the overall group mean for all outcomes combined (x=4.18) and rated 4 or more on a 5-point Likert-type scale for importance of inclusion in a minimum data set of outcome measures by at least 70 percent of respondents. Three outcomes were collapsed into a single outcome so that the final minimum set includes 48 outcomes.Given the inconsistencies in the choice of outcome measures routinely collected and reported in randomized evaluations of maternity care, it is hoped that use of the data set will increase the potential for national and international comparisons of models for maternity care. Although not intended to be prescriptive or to inhibit the collection of other outcomes, we hope that the core set will make it easier to assess the care of women and their babies during pregnancy and childbirth.