What we know already Patient reported outcome measures (PROMs) are an increasingly popular and prevalent method of ascertaining the impact of an intervention in health. For example there are PROMs measuring the success of intervention in diabetes, surgery and mental health. There is currently no such measure of specialist spiritual care. What this paper adds This paper describes the development of the Lothian spiritual care PROM from the literature. It shows where the items within the PROM came from and how they fit with current spiritual care theory. Why this is important. It is important to ground any PROM in a well developed theoretical understanding of what it is supposed to measure. Without this, the measure may be unreliable, so considerable effort needs to be devoted to the underpinning philosophy. This applies to any scale development. Any valid scale needs to be situated in a testable conceptual model. How this impacts upon chaplaincy The PROM that is constructed from this process is likely to be a valid measure of the impact of what chaplains do. A valid measure of specialist spiritual care is consistent with developing the evidence base for chaplaincy and could help service planning in a structured manner.