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Background: Orthostatic headache (OH) is a common feature of various conditions, including spontaneous intracranial hypotension (SIH), but no precise definition currently exists outlining the typical OH characteristics. This ambiguity risks misdiagnosis with unnecessary investigations and delay in institution of treatment. The present study aimed to carry out structured phenotyping of OH in patients with SIH with the aim of outlining its typical characteristics., Methods: Eligible patients with clinico-radiological confirmed SIH underwent a structured interview, after which a specialist interest group utilised the modified Delphi process to analyse the data and achieve consensus on defining the typical characteristics of OH in SIH., Results: In total, 137 patients were recruited. OH was present in 75.9%. Typical OH characteristics in SIH were defined as having a baseline severity (lying flat) on waking up of ≤3 (0-10, verbal response scale), headache onset-time of ≤4.5 h on becoming upright, time to peak severity of ≤7.5 h and an offset to baseline severity within 1.5 h of recumbency. Intra-individual consistency in the onset and offset-time was deemed a necessary characteristic., Conclusions: Defining typical OH characteristics has the potential of enhancing SIH diagnostics and management, at the same time as minimising unwarranted invasive procedures., Competing Interests: Declaration of conflicting interestsDM, SC, SG, SK, PS, AT, CD, AQ, ID and JW have no competing interests.MSM is chair of the medical advisory board of the CSF Leak Association; has served on advisory boards for Allergan, Autonomic Technologies Inc, Eli Lilly, Novartis, Pfizer, Salvia and TEVA; has received payment for educational presentations from Allergan, electroCore, Eli Lilly, Novartis and TEVA; has received grants from Abbott, Medtronic and electroCore; and has a patent on system and method for diagnosing and treating headaches (WO2018051103A1, issued). JA has received remuneration for consultancy advice and education provision from Allergan/AbbVie and TEVA. HA-L has lectures and education paid by International Medical Press, Sanofi and Eisai. BD has received remuneration for consultancy advice and education provision from TEVA, Allergan and Lilly. PJD has received fees or educational support from Abbvie, Lilly, Novartis, Pfizer and TEVA, and has shareholdings in Novo Nordisk, Lilly, Regeneron, Alnylam and Ionis Pharma. SL has received fees for attending advisory meetings, presentations and preparing presentation materials from Abbvie, TEVA, Eli Lilly, Tillots Pharma, Salvia and Novartis. CJ is a member of CSF Leak Association. JDR has received funding from a Miriam Marks Brain Research UK Senior Fellowship, an MRC Clinician Scientist Fellowship (MR/M008525/1) and the NIHR Rare Disease Translational Research Collaboration (BRC149/NS/MH), as well as the MRC UK GENFI grant (MR/M023664/1), the Bluefield Project and the JPND GENFI-PROX grant (2019-02248).