Serum concentrations of estrone, androstenedione, testosterone, and sex hormone-binding globulin (SHBG) were measured postoperatively in 122 postmenopausal women with incident breast cancer and 122 age-matched population controls. After mutual adjustment, through conditional logistic regression, between the hormonal variables and body mass index (BMI), the odds ratios for increasing control-defined quartiles of estrone and androstenedione, respectively, were 1.00, 1.44, 1.76, 1.94 and 1.00, 0.83, 0.97, 2.43; there was no association of testosterone with breast cancer risk. Moreover, the odds ratios for increasing quartiles of SHBG and BMI were 1.00, 0.72, 0.28, 0.25 and 1.00, 0.39, 0.28, 0.19, respectively. This study reveals sharp contrasts in breast cancer risk between women with high estrone and low BMI and SHBG, vs women with low estrone and high BMI and SHBG.