TGF-beta1 has a dual role in carcinogenesis. In this gene, a leucine to proline substitution in codon 10 leads to higher circulating levels of TGF-beta1. This variant has been studied in relationship to the risk for breast cancer yielding contradicting results. We aim to unravel the relationship of this polymorphism and the risk of breast cancer. Women participating in the Rotterdam Study including 143 patients with incident breast cancer were genotyped for this polymorphism. We carried out a logistic regression and a survival analysis using age as the time variable. The logistic regression analysis showed an increased risk of breast cancer for Proline carriers (OR=1.4; 95% confidence interval (CI)=1.1-2.0) versus non-carriers. The survival analysis showed that carriers of the same allele had an increased risk of breast cancer (HR=1.4, 95% CI=1.1-2.0) against non-carriers. Our data suggest that the TGF-beta1 Leu10Pro polymorphism might play a role in breast cancer risk.