Epidemiologic studies have linked diets high in vegetables and fruit with an increased likelihood of survival after the diagnosis of breast cancer, and clinical and epidemiologic studies have identified obesity as an important negative prognostic factor. Of the 26 studies published since 1990 that examined the relationship with obesity and survival, 17 reported a significant inverse relationship. Five of the eight cohort studies of breast cancer survivors that examined intakes of vegetables, fruit and related micronutrients published since 1985 reported a positive relationship between these factors and survival. The hypothesis that lifestyle factors such as diet and physical activity may improve the prognosis in women who have been diagnosed with breast cancer is currently under study. The Women's Healthy Eating and Living Study is a randomized controlled study that tests the effects of a diet high in vegetables, fruit and fiber and low in fat on disease-free survival after treatment for early stage breast cancer (n = 3109). In the Healthy Weight Management for Breast Cancer Survivors Study, a multifaceted approach to promoting weight loss and long-term weight maintenance is being tested in 85 women at risk for breast cancer recurrence. The intervention emphasizes increased physical activity, strategies to improve body image and self-acceptance, and cognitive-behavioral therapy to promote healthy eating attitudes and behaviors. The results of these studies will contribute to understanding the roles of diet and physical activity in the progression of breast cancer.