Introduction: TRS is recommended for children who have macroglossia associated with BWS to overcome or reduce the secondary negative functional effects of the macroglossia on speech, drooling, oral motor skills, feeding and appearance. However, few studies describe the exact nature of these functional effects and the degree of improvement that is achieved post surgically. Furthermore, only two small studies to date, report on the functional and psychosocial profiles both pre and post operatively within the same cohort of children using defined outcome measures (Shipster et. al. 2006; 2012). In contrast, this study carried out at the UK national center for this patient group, describe systematically the pre-operative functional and psychosocial effects of the macroglossia and the changes that occur post-operatively using the same set of outcome measures both pre and post surgically. It also discusses the genotype of the participants and the optimal age to perform the surgery. This study expands on a previous report of 87 patients who underwent TRS in the same center. This is the largest cohort studied to date. Methods: Between 2003 and 2018, a consecutive series of 146 participants with a genetically confirmed diagnosis of BWS underwent a modified key hole excision TRS. This was a primary procedure for 138 participants and a secondary procedure for 8 participants. Age at surgery ranged between 1 and 17 years. 85 % had surgery below 3 years of age. All were evaluated pre-operatively and 3–8 months post-operatively. Data was also collected on co-morbid factors which could affect the functional outcomes. Results: A significant improvement (<0.05) was obtained post surgically for every functional outcome measured. Anterior speech errors and oral stage feeding difficulties were present in the majority pre-operatively and were eliminated by TRS. Excessive drooling was present in 80% pre-operatively and significantly reduced or eliminated post-operatively. Positive psychosocial changes and satisfaction with the functional changes following surgery was reported in all cases. Speech impairment and feeding difficulties unrelated to the macroglossia also occurred in the cohort. Conclusion: Macroglossia causes distinct speech and feeding difficulties; increased drooling and psychosocial difficulties due to the enlarged tongue and the functional difficulties that arise as a direct consequence of the macroglossia. TRS has a positive impact on these difficulties with consistently good outcomes for children with BWS.