Background <p>Upper limb spasticity is a common condition in paediatric patients, often resulting from neurological disorders such as cerebral palsy, traumatic brain injury, or stroke. There are currently no standardised outcome measures to assess progress after interventions for upper limb spasticity in children. Wide variation in currently reported outcomes makes comparison of treatments difficult. This study aims to identify outcome measures that have previously been reported in studies evaluating the management of upper limb spasticity in children and to facilitate the development of a consensus core outcome set (COS) suitable for use in all future studies of upper limb spasticity in children.</p> Methods/design <p>This study will include a systematic review of the academic literature to identify a list of outcome measures that have previously been reported. The list of outcome measures will be used in a consensus setting exercise with focus groups of key stakeholders to identify key outcomes. A Delphi process to include two rounds will then be used to define the most important outcomes to all stakeholders forming the COS.</p> Discussion <p>Core outcomes represent the minimum expected data reported for a specific condition and will improve the quality of future studies, reducing bias, allowing easier comparison and enhancing opportunities for larger meta-analysis and more meaningful future research.</p> Trial registration <p>Core Outcome Measures in Effectiveness Trials Initiative (COMET). Registered on 20 Jan 2024.</p> <p>Prospero International prospective register of systematic reviews, registration number: CRD42024536296. Registered on 17 April 2024.</p>