Phytoestrogens are found in foods such as soy (isoflavones) and flaxseed (lignans), and certain botanical supplements. Their role in estrogen receptor positive (ER+) breast cancer recurrence and treatment is controversial, and it is unknown how this affects intake among patients. The Ontario Cancer Registry was used to identify 417 population-based breast cancer cases (mean time from diagnosis was 57 days). A questionnaire was mailed to determine intake of phytoestrogen foods and supplements in the last 2 mo, changes since diagnosis and differences by ER tumor status or hormonal treatment. Of 278 (67%) respondents, 56% consumed soy foods, 39% consumed isoflavone-rich foods (tofu, soybeans, soy milk, soy nuts), and 70% ate lignan-rich foods, including flaxseed (33%). Only soy milk, flaxseed, and flaxseed bread were commonly consumed more than once/wk. Few patients (4%) took isoflavone (soy, red clover, kudzu, licorice, isoflavones) or lignan/flaxseed supplements. Since diagnosis, 17% started or stopped soy foods (most stopped); this was more prevalent among those receiving hormonal treatment (20%; 95% confidence interval (CI): 14, 26) than not (6%; 95% CI: 1, 12). No other differences by ER status or hormonal treatment were observed. Research is needed to confirm this and to explore influencing factors.