Background: Intakes of dietary iron and, in particular, heme iron may increase breast cancer risk because of the prooxidant properties of iron. However, few studies have examined the association of iron and heme-iron intakes with breast cancer risk. Objective: We assessed the association of intakes of dietary iron and heme iron with risk of postmenopausal breast cancer. Design: We used data from the National Institutes of Health-AARP Diet and Health Study to assess intakes of total dietary iron, iron from meat, iron from red meat, and heme iron in relation to breast cancer risk in 116,674 postmenopausal women who completed a detailed questionnaire regarding meat preparation methods and degrees of doneness. During 6.5 y of follow-up, 3396 cases of invasive breast cancer were identified. Cox proportional hazards models were used to compute hazard ratios (HRs) and 95% CIs. Results: After adjustment for covariates, HRs for the highest compared with the lowest quintiles of intakes of total iron, iron from meat, iron from red meat, and heme iron were all close to unity, and there were no increasing trends with increasing intakes. The multivariable-adjusted HR for the highest compared with the lowest quintile of heme-iron intake was 1.01 (95% CI: 0.89, 1.14; P for trend = 0.97). In addition, no associations were seen when iron variables were stratified by possible effect modifiers or hormone receptor status. Conclusion: The results of this large cohort study do not support an association between iron or heme-iron intakes and postmenopausal breast cancer.