Epidemiological studies have identified body weight as a risk factor for breast cancer. Beyond the amount of adipose tissue a woman has, its distribution, particularly abdominally, may be a risk factor in breast cancer etiology. Body fat distribution is commonly measured by a waist-to-hip circumference ratio lpar;WHR). We performed a meta-analysis to summarize the published literature on WHR and breast cancer risk. After assembling all published studies, we extracted mean WHRs for study participants and adjusted risk estimates comparing highest with lowest partition of WHR and calculated weighted mean differences in WHR between cases and noncases and summary risk estimates based on study design and menopausal status. The weighted mean difference was 0.016 [95% confidence interval (CI) = 0.005-0.028] for all studies combined. The summary risk estimates were 1.80 (95% CI = 1.29-2.50) for case-control studies and 1.27 (95% CI = 1.07-1.51) for cohort studies. By menopausal status, the summary risks were 1.79 (95% CI = 1.22-2.62) for premenopausal women and 1.50 (95% CI = 1.10-2.04) for postmenopausal women. For all studies combined, the summary risk was 1.62 (95% CI = 1.28-2.04). This meta-analysis indicates that a greater WHR is associated with increased risk of breast cancer and suggests that the avoidance of abdominal obesity may reduce risk of the disease.