Background: The WBRTMel trial is a multinational, open-label, phase III randomised controlled trial comparing whole brain radiotherapy (WBRT) to observation following local treatment of one to three melanoma brain metastases with surgery and/or stereotactic irradiation. The primary trial endpoint was to determine the effect of adding WBRT to local treatment on distant intracranial control, and the secondary endpoints were neurocognitive function, quality of life (QoL), performance status, overall survival, death from intracranial causes, death from melanoma and cost-effectiveness. Objective: The objective of this update is to outline and publish the pre-determined statistical analysis plan (SAP) before the database lock and the start of analysis. Methods: The SAP describes basic analysis principles, methods for dealing with a range of commonly encountered data analysis issues and the specific statistical procedures for analysing efficacy and safety outcomes. The SAP was approved after closure of recruitment and before completion of patient follow-up. It outlines the planned primary analyses and a range of subgroup and sensitivity analyses regarding the clinical and QoL outcomes. Health economic outcomes are not included in this plan but will be analysed separately. The SAP will be adhered to for the final data analysis of this trial to avoid analysis bias arising from knowledge of the data. Results: The resulting SAP is consistent with best practice and will allow open and transparent reporting. Conclusion: We have developed a SAP for the WBRTMel trial which will be followed to ensure high-quality standards of internal validity to minimise analysis bias. Trial registration: ANZ Clinical Trials Registry, ACTRN12607000512426. Registered on 9 October 2007. ClinicalTrials.gov, NCT01503827. Registered on 4 January 2012. Trial group reference numbers ANZMTG 01.07, TROG 08.05.