Obesity increases breast cancer risk in post-menopausal women. This is, in part, due to elevated non-glandular aromatase activity, resulting in higher estradiol serum levels. We tested the hypothesis that obesity and menopausal status influence the intra-tumoral estrogen system of breast cancer tissue.Breast cancer tissue and fasting serum were collected from 26 female patients. After microdissection of the frozen samples, RNA was isolated, and expression of estrogen receptor (ER)alpha, ERbeta1, ERbeta2, ERbeta5, CYP19 aromatase and steroid sulfatase was measured on mRNA level by means of real time RT-PCR. Fasting estradiol serum levels were analysed by ELISA.Post-menopausal women older than 70 years exhibited a significantly higher expression both of steroid sulfatase and ERalpha than did pre-menopausal women younger than 50 years. We identified a significant positive correlation between body mass index (BMI) and lymphovascular/vascular invasion. A significant inverse correlation between ERalpha and ERbeta2 expression was identified in invasive breast cancer tissue irrespective of BMI or menopausal status.In conclusion, we report an association between menopausal status - but not BMI - and the intra-tumoral expression of steroid sulfatase and ERalpha. Our observation that BMI was associated with invasiveness supports the hypothesis that metabolic factors are able to affect essential features of breast cancer.