Background— Obesity is associated with heart failure (HF) incidence. We examined the strength of the association of body mass index (BMI) with HF by age and joint associations of BMI and waist circumference (WC). Methods and Results— Women aged 48 to 83 (n=36873) and men aged 45 to 79 (n=43487) self-reported height, weight, and WC. HF hospitalization or death (n=382 women, 718 men) between January 1, 1998, and December 31, 2004, was determined through administrative registers. Hazard ratios, from Cox proportional-hazards models, for an interquartile range higher BMI were 1.39 (95% CI, 1.15 to 1.68) at age 60 and 1.13 (95% CI, 1.02 to 1.27) at 75 in women. In men, hazard ratios were 1.54 (95% CI, 1.37 to 1.73) at 60 and 1.25 (95% CI, 1.16 to 1.35) at 75. A 10-cm higher WC was associated with 15% (95% CI, 2% to 31%) and 18% (95% CI, 4% to 33%) higher HF rates among women with BMI 25 and 30 kg/m ² , respectively; hazard ratios for 1 kg/m ² higher BMI were 1.00 (95% CI, 0.96 to 1.04) and 1.01 (95% CI, 0.98 to 1.04) for WC 70 and 100 cm, respectively. In men, a 10-cm higher WC was associated with 16% and 18% higher rates for BMI 25 and 30 kg/m ² , respectively; a 1 kg/m ² higher BMI was associated with 4% higher HF rates regardless of WC. Conclusions— Strength of the association between BMI and HF events declined with age. In women, higher WC was associated with HF at all levels of BMI. Both BMI and WC were predictors among men.