Consumer involvement in NHS research is Department of Health policy within the UK. Despite the existence of policy directives and guidance, until recently there has been no consensus among consumers and researchers about what it means to involve consumers successfully in NHS research. This paper discusses the value of consensus research in this policy area, and presents the detailed findings of a Delphi study carried out to reach consensus on principles and indicators of successful consumer involvement in NHS research. Study participants, comprising consumers, researchers and consumer-researchers, were identified using a purposive sampling strategy. Consensus was reached on eight clear and valid principles of successful consumer involvement in NHS research, with each principle having at least one clear and valid indicator. Subgroup analysis revealed few significant differences in how consumers, researchers and consumer-researchers rated the principles and indicators. The implications and limitations of the study are discussed. Further research is needed to assess: (1) the usefulness of the principles and indicators for differing models of consumer involvement, health research methodologies, and subject areas within health research; and (2) the impact of 'successful' consumer involvement on health research processes and outcomes.