BACKGROUND: The differences in the incidence of heart failure by race/ethnicity and the potential mechanisms for these differences are largely unexplored in women. METHODS AND RESULTS: A total of 156 143 postmenopausal women free of self-reported heart failure enrolled from 1993 to 1998 at 40 clinical centers throughout the United States as part of the Women's Health Initiative and were followed up until 2005, for an average of 7.8 years, for incident hospitalized heart failure. Incident rates, hazard ratios (HRs), and 95% confidence intervals were determined by use of the Cox proportional hazard model comparing racial/ethnic groups, and population-attributable risk percentages were calculated for each racial/ethnic group. Blacks had the highest age-adjusted incidence of heart failure (380 in 100 000 person-years), followed by whites (274), Hispanics (193), and Asian/Pacific Islanders (103). The excess risk in blacks compared with whites (age-adjusted HR=1.45) was significantly attenuated by adjustment for household income (HR=0.97) and diabetes mellitus (HR=0.89), but the lower risk in Hispanics (age-adjusted HR=0.72) and Asian/Pacific Islanders (age-adjusted HR=0.44) remained despite adjustment for traditional risk factors, socioeconomic status, lifestyle, and access-to-care variables. The effect of adjustment for interim coronary heart disease on nonwhite versus white HRs for heart failure differed by race/ethnic group. CONCLUSIONS: Asian/Pacific Islander and Hispanic women have a lower incidence of heart failure and black women have higher rates of heart failure compared with white women. The excess risk of incident heart failure in black women is explained largely by adjustment for lower household incomes and diabetes mellitus in black women, whereas the lower rates of heart failure in Asian/Pacific Islanders and Hispanics are largely unexplained by the risk factors measured in this study. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00000611.