BACKGROUND: Breast cancer (BC) is the most prevalent cancer in Iranian women and the fifth most common cause of cancer-related death in Iran. Among predicting factors and preventive measures for BC, the parity and breastfeeding (BF) are controversial issues. We therefore conducted this case-control study to find out the relation of parity and BF to incidence and risk of BC. METHOD: A structured questionnaire that covered demographic criteria and BC risk factors was completed for case (376 cases) and control (425 subjects) groups, both matched in terms of demographic variants, reproductive issues, and socioeconomic status. Odds ratio (OR) and 95% confidence intervals (CI) were computed as measures of association from the logistic models. All p values reported are two-sided. RESULTS: Parity significantly reduces the risk of BC (p