Lignans are natural plant compounds with estrogenic properties and are probably the most important source of phytoestrogens in western diets. They have been suggested to have anticarcinogenic potential. For an evaluation of the effect of these compounds, namely enterolactone, on breast cancer risk, we have reviewed the literature available on major epidemiological studies. We analyzed methodological issues, the design and results of 3 studies providing data on enterolactone dietary intake, 3 studies on urinary excretion and 4 studies concerning blood measurements of enterolactone. All studies on dietary intake were retrospective and based on questionnaires. Two studies showed a significant inverse relationship between dietary lignans consumption and breast cancer incidence, specifically in premenopausal women. No effect was evident in the third study. Among the urinary enterolactone excretion studies, two studies (one retrospective, the other prospective) showed a definite protective effect. However, one retrospective study failed to show any significant interaction. Again, conflicting results were obtained from enterolactone blood measurement studies: two studies demonstrated a protective effect due to enterolactone in premenopausal women, while the other two studies failed to demonstrate any association. In summary, epidemiological evidence to date is conflicting. Prospective large scale studies will require assessing the consumption of antibiotics and dietary habits during adolescence in order to obtain definitive conclusions.