Histological tumor grade is a well-established marker of breast tumor aggressiveness and prognosis. A number of reproductive factors, including parity and age at first birth, have been shown to be related to breast cancer risk, but few studies have examined the association of these variables with breast cancer aggressiveness. In this study, 813 newly diagnosed breast cancer patients were surveyed for demographic and lifestyle characteristics. Tumor grade and other clinical variables were abstracted from medical records. Multivariate logistic regressions were performed with each reproductive factor as the independent variable of interest. Regressions were also stratified on menopausal status, hormone therapy use, and tumor receptor status. None of the reproductive factors examined including age of first period, number of pregnancies, number of births, and hormone usage was statistically significantly associated with tumor grade. Although more studies are needed to determine whether other factors unexplored in this study are related to tumor aggressiveness, our study indicates that these factors do not predict the aggressiveness of breast cancers.