A total of 512 breast cancer patients and 540 controls were compared to examine the risk factors for different categories of breast cancer as defined by age, menopausal status and estrogen receptor (ER) tumor status. Significant differences were found by menopausal status, for age at first birth and age at menarche for all women, and for age at first birth and family history for women between 45 and 54 years old. No significant differences were found with ER status alone; however there was a significant difference between ER status and body weight in premenopausal women; the above significant differences with menopausal status were not found when stratified by ER tumour status. These findings support the hypothesis for aetiological differences for pre- and postmenopausal breast cancer and suggest that ER tumour status may influence the risk associated with body weight.