AIMS: No studies have examined the effect of mineralocorticoid receptor antagonist therapy on new-onset diabetes. In addition, though the combination of diabetes and chronic heart failure (CHF) carries a poor prognosis, few studies have examined predictors of new-onset diabetes in those with CHF. METHODS AND RESULTS: In patients with symptomatically mild CHF who participated in the placebo-controlled Eplerenone in Mild Patients Hospitalization and Survival Study in Heart Failure, we examined the effect of the aldosterone antagonist, eplerenone, on physician-diagnosed diabetes using univariate Cox proportional hazard analysis. To identify predictors of new-onset diabetes (measures of glycaemia were not available), data from trial arms were combined and multivariate Cox proportional hazard analyses and receiver operating characteristic curve analyses were conducted. At baseline, the mean age of 1846 initially non-diabetic patients was 69 years and mean left ventricular ejection fraction was 26%. Over 21 months, 69 (3.7%) developed diabetes (33 on eplerenone, 36 on placebo). Eplerenone had no effect on new-onset diabetes [hazard ratio (HR) 0.94, 95% confidence interval (CI) 0.59-1.52] and no effect on the composite of new-onset diabetes or mortality (HR 0.80, 95% CI 0.64-1.01). Independent predictors of new-onset diabetes included digoxin therapy, higher serum alanine aminotransferase, longer duration of heart failure, current or previous smoker, higher waist circumference, lower age, and higher systolic blood pressure with a combined c-statistic of 0.74. CONCLUSIONS: Eplerenone had no effect on new-onset diabetes in patients with CHF, but further large-scale studies are required to address this question comprehensively. Commonly recorded parameters provided useful information for predicting new-onset diabetes.