Limited epidemiological evidence suggests that calcium intake may be related to breast cancer risk. Data from a large, population-based, case-control study (n = 1,459 cases, 1,556 controls) conducted in Shanghai, China, between 1996 and 1998 were used to investigate the association between calcium intake and risk for breast cancer. Diet was assessed using a quantitative food-frequency questionnaire. The multivariate-adjusted odds ratio (OR) comparing all women combined in the highest to lowest deciles of total calcium intake was 0.74 (95% confidence interval [CI] = 0.46-1.20). Whereas calcium primarily derived from poultry was inversely associated with risk for breast cancer (comparing the highest to lowest quintile OR = 0.71, 95% CI = 0.55-0.93) with a statistically significant test for trend, calcium derived from milk, seafood, fruit, and vegetables was not associated with risk of breast cancer. Given that breast cancer is one of the top contributors to cancer incidence worldwide, even a moderate inverse association between calcium and breast cancer risk, if confirmed, could have important public health implications in breast cancer prevention.