Using data from 66 countries, we conducted an international comparison study to identify the most important predictors of female breast cancer mortality rates. This study was unique in that it included data on per capita tobacco disappearance, alcohol consumption, socioeconomic status (SES), reproductive factors, and a wide array of nutritional data. Results of correlation and single independent-variable linear regression models indicated that breast cancer mortality was most strongly associated with dietary factors typically associated with affluence, especially animal products. The strongest negative (i.e., protective) associations were with those variables related to increased fertility and population growth. A multiple linear regression that accounted for all important predictors simultaneously explained 91% of the variability in mortality rates across these countries. This model indicated a strong positive association between breast cancer mortality and calories from animal sources. Fish and cereal products as well as annual percentage growth in population appeared to exert protective effects. Despite the limitations of this type of analysis, the observed effect of high meat and animal product consumption, the major contributor to variability in dietary fat, as well as the protective effect of increased fertility are consistent with the known biology of breast cancer. The protective effect of fish and cereal consumption that we observed will require further study.