To investigate risk factors for breast cancer in Taiwan, a low-incidence area, a case-control study was conducted. This comprised 244 subjects with diagnosed and pathologically confirmed breast cancer (age range 20-80 years) and 450 female ophthalmology outpatients as controls. Univariate and multiple logistic regression analysis suggests that breast cancer in Taiwan is aetiologically similar to breast cancer in high to moderate-incidence areas. A family history of breast cancer appears to be the most important factor contributing to the risk of breast cancer (odds ratio = 4.69). The effect of reproductive hormones (represented by the years of history of menses in premenopausal women, odds ratio = 3.35; or the age at menarche in post-menopausal women, odds ratio = 2.67) plays a significant role in tumorigenesis. Breast feeding appears to be a particularly important protective factor in Taiwanese women (odds ratio = 0.57).