The Fundamentals of Care Framework is an evidence‐based, theory‐informed framework that conceptualises high‐quality fundamental care. The Framework places the nurse–patient relationship at the centre of care provision and outlines the nurse behaviours required for relationship development. Numerous instruments exist to measure behavioural aspects of the nurse–patient relationship; however, the literature offers little guidance on which instruments are psychometrically sound and best measure the core relationship elements of the Fundamentals of Care Framework. This study evaluated the quality of nurse–patient relationship instruments (...) by (1) assessing their content development and measurement properties (e.g. dimensionality, targeting, reliability, validity) and (2) mapping instrument content to the Framework's core relationship elements: trust, focus, anticipate, know, and evaluate. Twenty‐seven instruments were evaluated. Findings demonstrated that patients and nurses were rarely involved in item development. Most instruments exhibited poor measurement properties, with only one instrument having complete information on all quality indicators. Instrument content focused primarily on nurses getting to know patients and earning their trust, with only 54, 18, and 1 item(s), respectively, measuring ‘focus’, ‘anticipate’ and ‘evaluate’. Hence, there does not appear to be a robust instrument measuring behavioural aspects of nurse–patient relationships, nor one capturing the relationship elements of the Fundamentals of Care Framework. (shrink)