Context Understanding the effects of burosumab compared to conventional therapy or no treatment on patient-important outcomes in adults with X-linked hypophosphatemia (XLH) is essential to guide evidence-based treatment recommendations.Objective To examine the highest certainty evidence addressing the management of XLH in adults to inform treatment recommendations.Methods We searched Embase, MEDLINE, Web of Science, and Cochrane Central up to May 2023. Eligible studies included randomized controlled trials (RCTs) and observational studies of individuals aged 18+ with clinically or genetically confirmed XLH. Manuscripts comparing burosumab to no treatment or conventional therapy (phosphate and active vitamin D) and conventional therapy to no treatment were included. Two reviewers independently determined eligibility, extracted data, and assessed risk of bias (RoB). GRADE methodology was used to assess evidence certainty.Results We screened 4114 records, after removing duplicates, and assessed 254 full texts. One RCT and 2 observational studies were eligible. The RCT of burosumab vs no treatment had low RoB. Burosumab probably improves pain from fracture/pseudofracture healing (moderate certainty) but has little or no impact on direct pain measures (moderate certainty). Burosumab may reduce the need for parathyroidectomy (low certainty) but has little or no impact on fatigue (high certainty), stiffness (moderate certainty), and mobility (low certainty) over 24 weeks. Burosumab may increase dental abscess risk (low certainty). Indirect evidence comparing burosumab to conventional therapy provided low certainty regarding burosumab vs conventional therapy. Two observational studies on conventional therapy vs no treatment had high RoB and very low certainty regarding the impact of conventional therapy on patient-important outcomes.Conclusion No formal comparisons between burosumab and conventional therapy in adults exist. Evidence for conventional therapy vs no treatment is very uncertain. Our review highlights the need for more data on the long-term effects of burosumab and conventional therapy on patient-important outcomes in adult patients with XLH.