Background: In chronic central serous chorioretinopathy (CSCR), fluid accumulates in the sub-retinal space. It is a common visually disabling condition in individuals of working age. There is no definitive treatment. Previous research suggests the mineralocorticoid receptor antagonist, eplerenone, is effective for treating CSCR but it is not licensed for this indication. We evaluated whether eplerenone is superior to placebo for treating chronic CSCR. Methods: We conducted a placebo-controlled parallel-group randomised trial in 22 United Kingdom hospitals. Participants were aged ≥18 and ≤60 years with treatment naïve CSCR for ≥4 months. Randomisation stratified by best-corrected visual acuity (BCVA) and hospital was performed online, with participants randomised to receive oral eplerenone (25 mg/day for one week, increasing to 50 mg/day for up to 12 months) plus usual care or placebo plus usual care. Participants, care teams, outcome assessors, pharmacists and the trial management group were masked. The primary outcome was BCVA at 12 months. All outcomes apart from safety were analysed on a modified intention-to-treat basis. The trial is registered: ISRCTN92746680.Findings:Between 11/01/2017 and 22/02/2018, 57 participants were randomised to eplerenone and 57 to placebo; 57 and54 participants respectively were included in the final analysis. Modelled mean BCVA at 12 months in the placebo and eplerenone groups were 79.5 (SD 4.5) and 80.4 (SD 4.6) letters, with an adjusted estimated difference (eplerenone minus placebo) of 1.73 letters (95% confidence interval -1.12 to 4.57, p=0ꞏ24) at 12months. Hyperkalaemia occurred in eight participants in each group (14%). No serious adverse events occurred in the eplerenone group; three unrelated serious adverse events occurred in the placebo group. Interpretation: Eplerenone was not superior to placebo in improving BCVA in people with chronic CSCR during 12 months follow-up. Funding Efficacy and Mechanism Evaluation Programme, National Institute for Health Research and Social Care.