PURPOSE: Hip microinstability is a relatively new diagnosis which is increasingly being discussed in the literature and yet there are no clear guidelines for making a diagnosis. Microinstability has generally been defined as persistent excessive hip motion that has become symptomatic especially with pain. This aim of this Delphi study was to seek expert opinion to formulate a diagnostic criteria for hip microinstability. METHODS: A Delphi methodology was used for this consensus study. A literature search was conducted on PubMed up to March 2019 using the keywords ((hip) and (microinstability)) to identify relevant articles on this topic. All relevant criteria used for diagnosing hip microinstability were collated to create a questionnaire and further criterion suggested by the experts were included as well. Four rounds of questionnaires were delivered via an online survey platform. Between each round the authors acted as administrating intermediaries, providing the experts with a summary of results and synthesising the next questionnaire. The expert panel was comprised of 27 members: 24 (89%) orthopaedic surgeons and 3 (11%) physiotherapists from around the world. RESULTS: Expert panel participation in rounds 1-4 was: 27 (100%), 20 (74%), 21 (78%) and 26 (96%) respectively. A literature review by the authors identified 32 diagnostic criteria to populate the first questionnaire. Experts suggested amending three criteria and creating five new criteria. The panel converged on ranking 3 (8%) of criteria as "Not important", 20 (54%) as "Minor Factors" and 14 (38%) as "Major Factors". No criteria was ranked as "Essential". Criteria were subcategorised into patient history, examination and imaging. Experts voted for a minimum requirement of four criteria in each subcategory, including at least six "Major factors". The final diagnostic tool was approved by 20 (77%) of the final round panel. CONCLUSION: This study describes the first known expert consensus on diagnosing hip microinstability. The relative complexity of the final diagnostic tool is illustrative of the difficulty clinicians' face when making this diagnosis. LEVEL OF EVIDENCE: V.