More than one million new patients suffer from breast cancer annually in the world. In developed countries,breast cancer is the most common malignancy diagnosed among women, and in developing regions, it oftenranks second to cervical cancer. This study aimed to investigate the relationship between incidence of breastcancer and reproductive factors in North-West of Iran. This retrospective analytical control-case study wasconducted with 235 breast cancer patients and 235 women in the control group. Data collection tools includeda set of questions with interviews and patient medical records. Data were analyzed using statistical tests: t-test,Chi-square, Fisher, and Pearson correlation coefficient. Significantly increased risks were associated betweenbreast cancer and older age at first pregnancy, age at menopause and history of contraceptive use. A trend fordecreasing risk were observed with increasing parity. Findings of this study showed no association between breastcancer and age at menarche. The study results suggested that physiological and reproductive factors may playimportant roles in the development breast cancer among Iranian women.