Abstract: Breast cancer characteristics vary in racial/ethnic groups. Reproductive risk factors have been associated with estrogen receptor positive disease. We examined the association between reproductive risk factors and receptor status in different racial/ethnic groups to determine if some of the variation can be explained by a different reproductive risk profile. A retrospective chart review of all new breast cancer cases presenting to Elmhurst Hospital Center (Elmhurst, NY) between 1997 and 2004 was conducted. Data including patient characteristics and tumor characteristics were obtained. Four hundred ninety-nine patients were divided into two groups: the first group consisted of patients with estrogen positive disease and the second of those with estrogen negative disease. Association between reproductive risk factors and estrogen receptor status was examined for each racial group. There was a significant variability in patient age, age at menarche, parity, rates of nulliparity, age at first birth, and rates of menopause between the different ethnic groups. We found a strong, statistically significant association between reproductive risk factors and estrogen positive disease in the Asian group, where 96% of breast cancer patients who were either nulliparous or had late onset of first childbirth were found to have estrogen positive disease, whereas only 52% of those without these risk factors were found to be estrogen positive. For black patients the rates were 55% versus 56%, for Hispanic patients 64% versus 61%, and for non-Hispanic whites 74% versus 81%. In our patient population, differences in breast cancer characteristics could not be ascribed to a different reproductive risk pattern.