Introduction Postembolisation syndrome (PES) is the most common side effect of vascular embolisation of solid organs. Although prophylactic corticosteroids are known to reduce the incidence and severity of PES, no trials investigating their efficacy have been conducted in men undergoing prostatic artery embolisation (PAE). We postulate that steroids can have a similar effect in reducing PES after PAE. This paper describes the rationale and detailed protocol for a randomised controlled trial evaluating the efficacy of dexamethasone (DEXA) in reducing PES after PAE.Methods and analysis In this single-centre, randomised, double-blind, placebo-controlled trial, we will enrol 60 individuals undergoing PAE for benign prostatic hyperplasia. Participants will be randomised to receive IV DEXA (24 mg) or placebo (saline). The primary outcomes will be postprocedural fever, pain and quality of life. The secondary outcomes will include postprocedural nausea, postprocedural medicine usage, laboratory parameters (C reactive protein, prostate-specific antigen) and early PAE results.Ethics and dissemination Ethics approval was obtained from the Danish Committee on Health Research Ethics in the Capital Region (H-20025910). The results from this trial will be disseminated through publication in peer-reviewed journals and national and international presentations.Trial registration number Clinicaltrials.gov identifier: NCT04588857; EudraCT number: 2020-000915-53.