Aims Obesity is paradoxically associated with survival benefit in patients with chronic heart failure (HF). However, obesity complicates the management of diabetes mellitus (DM), which is common in HF. Yet, little is known about the impact of obesity in HF patients with DM. Therefore, we examined the association between obesity and outcomes in propensity-matched cohorts of HF patient with and without DM. Methods and results Of the 7788 participants with chronic mild to moderate HF in the Digitalis Investigation Group trial, 7379 were non-cachectic [body mass index (BMI) ≤20 kg/m2] at baseline. Of these, 2153 (29%) had DM, of whom 798 (37) were obese (BMI <30 kg/m 2). Of the 5226 patients without DM, 1162 (22%) were obese. Propensity scores for obesity were used to separately assemble 636 pairs of obese and non-obese patients with DM and 770 pairs of obese and non-obese patients without DM, who were balanced on 32 baseline characteristics. Among matched patients with DM, all-cause mortality occurred in 38 and 39 of obese and non-obese patients, respectively [hazard ratio (HR) when obesity was compared with no obesity 0.99; 95% confidence interval (CI) 0.801.22; P = 0.915]. Among matched patients without DM, all-cause mortality occurred in 23 and 27% obese and non-obese patients, respectively (HR associated with obesity 0.77; 95% CI 0.61-0.97; P = 0.025). ConclusionIn patients with chronic mild to moderate HF and DM, obesity confers no paradoxical survival benefit. Whether intentional weight loss may improve outcomes in these patients needs to be investigated in future prospective studies. © 2010 The Author.