Study summary: The present prospective study was designed to investigate the associations of caffeinated coffee and black tea consumption with risk of breast cancer overall and by hormone receptor status. The study included 61,433 women in the Swedish Mammography Cohort who were cancer free during the baseline enrollment period of 1987 to 1990. Coffee and tea intake was determined using a food-frequency questionnaire administered both at baseline and in 1997. Swedish cancer registers were accessed to obtain information concerning the incidence and nature of newly diagnosed invasive breast cancers in the study cohort. During an average follow-up period of 17.4 years (through year-end 2007), 2,952 incident cases of invasive breast cancer were found. Coffee consumption was found not to be associated with overall risk of breast cancer (multivariate relative risk (RR) for at least four cups per day compared to less than one cup per day = 1.02; 95% confidence interval (CI) = 0.87 - 1.20). Nor was any association found between coffee consumption and breast cancer subtype defined by estrogen receptor (ER) and progesterone receptor (PR) status. On the other hand, black tea intake was found to be significantly positively associated with risk of breast cancer overall and ER+/PR+ tumors in particular. The multivariate RRs comparing at least two cups of black tea per day with no consumption were 1.22 (95% CI = 1.05 - 1.42) for breast cancer overall and 1.36 (95% CI = 1.09 - 1.69) for ER+/PR+ breast cancer. The authors conclude that the study findings do not support a role of coffee consumption in the development of breast cancer. However, the results suggest that black tea may be positively associated with risk of ER+/PR+ breast cancer.