The authors investigated the association between overweight at the time of or soon after cancer diagnosis and survival in a cohort of 1,455 breast cancer patients aged 25-64 years. The patients were recruited into the Shanghai Breast Cancer Study (Shanghai, China), a population-based case-control study, between August 1996 and March 1998. The median follow-up time for this cohort was 5.1 years (1996-2002) after breast cancer diagnosis, and 240 deaths were identified. Being overweight at cancer diagnosis or soon afterward, as measured by body mass index (BMI; weight (kg)/height (m)(2)), was associated with poorer overall survival and disease-free survival. Five-year survival rates were 86.5%, 83.8%, and 80.1% for subjects whose BMIs were <23.0, 23.0-24.9, and >or=25.0, respectively (p = 0.02); the corresponding 5-year disease-free survival rates were 81.9%, 78.1%, and 76.6% (p = 0.05). The inverse association between BMI and survival persisted after adjustment for age at diagnosis and other known prognostic factors for breast cancer, including disease stage. The authors found neither waist:hip ratio nor waist circumference to be independently associated with overall survival or disease-free survival. These results suggest that excess weight may be an independent predictor of breast cancer survival among Chinese women.