Diabetes mellitus (DM) and chronic kidney disease (CKD) are common in patients with chronic heart failure (HF) and are associated with poor outcomes. However, the impact of multimorbidity due to DM and CKD on outcomes, relative to co-morbidity due to DM alone, has not been well studied in these patients. Of the 7,788 patients with chronic HF in the Digitalis Investigation Group trial, 2,218 had DM. We categorized these patients into those with DM alone (DM-only n = 1,123) and those with both DM and CKD (DM-CKD n = 1,095). Propensity scores for DM-CKD, calculated for each of the 2,218 patients, were used to match 699 pairs of patients with DM-only or DM-CKD. Matched Cox regression models were used to estimate associations between DM-CKD and outcomes. All-cause mortality occurred in 44% (rate 1,648/10,000 person-years) of patients with DM-CKD and 39% (rate 1,349/10,000 person-years of follow-up) of patients with DM-only (hazard ratio when DM-CKD was compared with DM-only 1.34, 95% confidence interval [CI] 1.11 to 1.62, p = 0.003). All-cause hospitalization occurred in 76% (rate 5,799/10,000 person-years) and 73% (rate 4,909/10,000 person-years) of patients with DM-CKD and DM-only, respectively (hazard ratio 1.16, 95% CI 0.99 to 1.36, p = 0.064). Respective hazard ratios for other outcomes were cardiovascular mortality 1.33 (95% CI 1.07 to 1.66, p = 0.010), HF mortality 1.41 (95% CI 1.02 to 1.96, p = 0.040), cardiovascular hospitalization 1.17 (95% CI 0.99 to 1.39, p = 0.064), and HF hospitalization 1.26 (95% CI 1.03 to 1.55, p = 0.026). In conclusion, compared with co-morbidity due to DM alone, the presence of multimorbidity due to DM and CKD was associated with increased mortality and morbidity in patients with chronic HF. © 2009 Elsevier Inc. All rights reserved.