Background: At present, the maternity care system in the Netherlands is being reorganized into an integrated model of care, shifting the focus of midwives to include increasing numbers of births in hospital settings and clients with medium risk profiles. In light of these changes, it is useful for midwives to have a tool which may help them in reflecting upon care practices that promote physiological childbirth practices. The Optimality Index-US is an evidence based tool, designed to measure optimal perinatal care processes and outcomes. It has been validated for use in the United States (OI-US), United Kingdom (OI-UK) and Turkey (OI-TR). The objective of this study was to adapt the OI-US for the Dutch maternity care setting (OI-NL). Methods: Translation and back translation were applied to create the OI-NL. A panel of maternity care experts (n = 10) provided input for face validation items in the OI-NL. Assessment of inter-rater reliability and ease of use was also conducted. Following this, the OI-NL was used prospectively to collect data on 266 women who commenced intrapartum care under the responsibility of a midwife. Twice groups were compared, based on parity and on care-setting at birth. Mean scores between these groups, corrected for perinatal background factors were assessed for discriminant validity. Results: Face validity was established for OI-NL on the basis of expert input. Discriminant validity was confirmed by conducting multiple regressions analyses for parity (beta = 6.21, P = 0.00) and for care-setting (beta = 12.1, p = 0.00). Interrater reliability was 98%, with one item (Apgar score) sensitive to scoring differences. Conclusion: OI-NL is a valid and reliable tool for use in the Dutch maternity care setting. In addition to its value for assessing evidence-based maternity care processes and outcomes, there is potential for use for learning and reflection. Against the backdrop of a changing maternity care system, and due to the specificity of its items OI-NL may be of value as a tool for ...