This article summarises the results of a review of the impact of research funded by the NHS Service Delivery and Organisation Research and Development (SDO) Programme. The review draws primarily on the HERG Payback model, and the outputs and outcomes of SDO research are summarised in each of the five Payback domains: service delivery, policy, practice, research and capacity building. The article also discusses conceptual and methodological problems in identifying and attributing research impact that have been raised by the SDO impact review. © The Policy Press.