BACKGROUND: Recent evidences showed that the phytoestrogen genistein positively affects bone metabolism with no clinically significant adverse effects in a cohort of osteopenic, postmenopausal women. However, there is still a knowledge gap regarding the long-term safety of genistein on the breast, the uterus, the thyroid gland and its efficacy in postmenopausal women. OBJECTIVE: To assess the safety profile of genistein on mammary and thyroid glands and endometrium and cardiovascular apparatus and its effects on bone metabolism after a 3-year therapy with pure, standardized genistein (54 mg/day).