Breast cancer is a common malignancy for women in most parts of the world and the incidence in Iranian women is growing. The patients are relatively younger than their western counterparts. The present hospital based casecontrol study was designed to determine roles of reproductive factors for breast cancer among women in Iran. Conducted at a teaching hospital in Tehran, Iranin 2004, the study covered a total of 303 cases of breast cancer and 303 healthy controls. Cases were identified through the Oncology Department of a university hospital and controls were collected from other wards or out-patient clinics at the same hospital. Control subjects were matched to patients for age. Informed consent was obtained from all cases and controls then demographic and reproductive factors were ascertained by in-person interview using a constructed questionnaire. Odds ratios and their 95% confidence intervals for breast cancer were derived using logistic regression analysis. The mean +SD ages of cases and controls were 48.8 + 9.8 and 50.2 + 11.1 years, respectively, (range 24-84). The final model for multiple analysis indicated that never married, post menopause, age at first live birth, number of live births, use of oral contraceptive pills, and history of chest X-rays between adolescence and 30 yrs of age, were significantly associated with breast cancer. Variables such as higher education, early age at menarche, abortion, breast feeding and its duration were not significant risk factors .