High social class has been linked to increased risk of breast cancer. The present study elaborates the associations between a frequently-used indicator of social class, length of education, and some reproductive factors associated with risk of breast cancer (age at menarche, the number of children, age at first pregnancy and use of oral contraceptives) in 8030 women in Tromsø, Norway. We found a weak negative association between level of education and age at menarche and a stronger negative association with parity. Women with high level of education tended to have their first pregnancy relatively late in life and more frequently reported ever use of oral contraceptives. These relationships support the notion that the difference in the incidence of breast cancer between women with high and low social class may be due to reproductive factors.