Associations between the risk of breast cancer and body-size indicators at the time of breast-cancer diagnosis were assessed among 328 pre-menopausal or post-menopausal cases and 417 controls participating in the Kuopio Breast Cancer Study. This case-control study follows the protocol of the international Collaborative Study of Breast and Colorectal Cancer. When the potential confounding factors were taken into account, tallness was related to increased risk of breast cancer, especially in post-menopausal women, whereas no clear association with body-mass index (BMI) was found. Waist-to-hip ratio (WHR) was the most important risk factor in both pre-menopausal and post-menopausal women. The post-menopausal cases with high positive estrogen-receptor status (ER++) had the highest weight and BMI; they had also the biggest weight gain since the age of 20. However, the association between WHR and breast cancer appeared to be independent of estrogen-receptor status. Our results suggest that WHR may be a better marker for breast cancer than the degree of adiposity.