In the cohort there were 427 cases of primary breast cancer in 488,989 person-years of observation. Breast cancer risk increased significantly with calendar period, with more than a doubling in rates from 1969-74 to 1990-94, independent of adjustment for reproductive factors and body mass index. Risk also increased significantly with increasing radiation dose to the breast, and according to traditional reproductive factors known to be associated with breast cancer. No significant association was seen between consumption of soya foods and risk of breast cancer. Specifically, the adjusted relative risk of breast cancer for tofu consumption 2-4 times per week was 0.99 (CI95 = 0.80-1.24) and for consumption 5 or more times per week was 1.07 (0.78-1.12), compared to consumption once a week or less. For miso soup the adjusted relative risks were 1.03 (0.81-1.31) for consumption 2-4 times per week and 0.87 (0.68-1.12) 5 or more times per week, compared to consumption once per week or less. These findings were similar for women across all ages and were not materially altered by adjustment for reproductive variables. Increasing dried fish consumption was associated with a significantly decreased risk of breast cancer and increasing pickled vegetable consumption was associated with a significantly increased risk of breast cancer. These associations were not prior hypotheses and may be due to chance.