Emerging evidence suggests that diet quality indices may serve as prognostic indicators of disease. However, the ability of these indices to predict breast cancer risk has not been evaluated previously. We assessed the association between several diet quality scores and the risk of breast cancer in postmenopausal women. The indices we used were the Healthy Eating Index (HEI), Alternate Healthy Eating Index (AHEI), Diet Quality Index-Revised (DQI-R), Recommended Food Score (RFS), and the alternate Mediterranean Diet Score (aMed). We calculated diet quality indices from dietary information collected in FFQ administered 5 times between 1984 and 1998 among women in the Nurses' Health Study cohort. Relative risks (RR) were computed using Cox proportional hazards models and adjusted for known risk factors for breast cancer. Separate analyses were conducted for estrogen receptor positive (ER+) and negative (ER-) tumors. Between 1984 and 2002, we documented 3,580 cases of breast cancer, of which 2,367 were ER+, and 575 were ER-. We did not observe any association between the diet quality indices and total or ER+ breast cancer risk. However, for ER- breast cancer, after adjusting for potential confounders, the RR comparing highest to lowest quintiles were 0.78 (95% CI=0.59-1.04, P for trend=0.01) for the AHEI, 0.69 (95% CI=0.51-0.94, P for trend=0.003) for the RFS, and 0.79 (95% CI=0.60-1.03, P for trend=0.03) for the aMed. These observations appeared to be the result of an inverse association (P for trend=0.01) with the vegetable component of the scores. We conclude that women who scored high in AHEI, RFS, and aMed had a lower risk of ER- breast cancer. The HEI and DQI-R appeared to be of limited value in predicting breast cancer risk.