Studies of risk factor differences between racial and ethnic groups within a population may be most valuable in delineating the etiology of breast cancer. Most studies of breast cancer risk factors have been conducted only among white women. We could not find any epidemiologic studies that investigated risk factors for breast cancer occurrence among Hispanic women. The Cancer and Steroid Hormone Study provided the opportunity to investigate risk factors for breast cancer among Hispanic women aged 20 to 54 years in a population-based case-control study of 148 case and 167 control subjects. The final multiple logistic regression analysis indicated that women who had a first-degree relative (mother or sister) with breast cancer were nearly twice as likely to have had breast cancer compared to women with no family history (OR = 1.89; 95% CI 1.10-3.16). Expected patterns of association between breast cancer and number of full-term pregnancies, age at first full-term birth, and benign breast disease, although not statistically significant, were observed. Unexpectedly, the results also suggested a reduced risk of breast cancer among Hispanic women associated with early age at menarche. These factors require further evaluation in larger studies among specific Hispanic subgroups.