Epidemiological evidence indicates that the association between body weight and breast cancer risk may differ across menopausal status as well as the estrogen receptor (ER) and progesterone receptor (PR) tumor status. To date, no meta-analysis has been conducted to assess the association between body weight and ER/PR defined breast cancer risk, taking into account menopausal status and study design. We searched MEDLINE for relevant studies published from January 1, 1970 through December 31, 2007. Summarized risk estimates with 95% confidence intervals (CIs) were calculated using a random-effects model. The summarized results of 9 cohorts and 22 case-control studies comparing the highest versus the reference categories of relative body weight showed that the risk for ER+PR+ tumors was 20% lower (95% CI=-30% to -8%) among premenopausal (2,643 cases) and 82% higher (95% CI=55-114%) among postmenopausal (5,469 cases) women. The dose-response meta-analysis of ER+PR+ tumors showed that each 5-unit increase in body mass index (BMI, kg/m2) was associated with a 33% increased risk among postmenopausal women (95% CI=20-48%) and 10% decreased risk among premenopausal women (95% CI=-18% to -1%). No associations were observed for ER-PR- or ER+PR- tumors. For discordant tumors ER+PR- (pre) and ER-PR+ (pre/post) the number of cases were too small (<200) to interpret results. The relation between body weight and breast cancer risk is critically dependent on the tumor's ER/PR status and the woman's menopausal status. Body weight control is the effective strategy for preventing ER+PR+ tumors after menopause.