Study summary: The present prospective study was designed to examine the association between red meat intake and breast cancer by hormone receptor status among premenopausal women. Study participants included 90,659 women ages 26 to 46 years in the Nurses' Health Study II. Red meat intake was determined by a food frequency questionnaire administered in 1991, 1995, and 1999. Respondents were followed up through year-end 2003. Breast cancer cases were self-reported and confirmed by review of pathologic reports. During a follow-up period of 12 years, 1,021 new cases of invasive breast carcinoma were documented. Greater red meat intake was found to be strongly associated with elevated risk of breast cancers that were estrogen and progesterone receptor positive (ER+/PR+; n = 512) but not to cancers that were estrogen and progesterone receptor negative (ER–/PR–; n = 167). Compared to those consuming fewer than four servings of red meat per week, the multivariate relative risks (95% confidence intervals) for ER+/PR+ tumors with increasing servings of red meat intake were (a) 1.42 (1.06-1.90) for five to seven servings per week; (b) 1.20 (0.89-1.63) for seven to 10 1/2 servings per week; and (c) 1.97 (1.35-2.88) for more than 10 1/2 servings per week (test for trend, P = .001). The corresponding relative risks for ER-/PR- breast cancer were 1.21 (0.73-2.00), 0.69 (0.39-1.23), and 0.89 (0.43-1.84) (test for trend, P = .28). The authors conclude that higher red meat intake may be a risk factor for ER+/PR+ breast cancer among premenopausal women.