Context: This study was performed to evaluate the effects of genistein on metabolic and cardiovascular risk factors in Caucasian postmenopausal subjects with metabolic syndrome (MetS). Objective: Our objective was to assess the effects of genistein on surrogate endpoints associated with diabetes and cardiovascular disease. Design and Setting: This was a randomized, double-blind, placebo-controlled trial at 3 university medical centers in Italy. Patients: Patients included 120 postmenopausal women with MetS according to modified Third Report of the National Cholesterol Education Program (NCEP), Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III) criteria. Intervention: After a 4-week stabilization period, postmenopausal women with MetS were randomly assigned to receive placebo (n = 60) or 54 mg genistein daily (n = 60) for 1 year. Main Outcome Measures: The primary outcome was homeostasis model assessment for insulin resistance (HOMA-IR) at 1 year. Secondary outcomes were fasting glucose, fasting insulin, total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides, visfatin, adiponectin, and homocysteine levels. Data on adverse events were also recorded. Results: At 1 year in genistein recipients, fasting glucose, fasting insulin, and HOMA-IR (mean from 4.5 to 2.7; P<.001) decreased and were unchanged in placebo recipients. Genistein statistically increased HDL-C (mean from 46.4 to 56.8 mg/dL) and adiponectin and decreased total cholesterol, LDL-C (mean from 108.8 to 78.7 mg/dL), triglycerides, visfatin, and homocysteine (mean from 14.3 to 11.7 μmol/L) blood levels. Systolic and diastolic blood pressure was also reduced in genistein recipients. Genistein recipients neither experienced more side adverse effects than placebo nor discontinued the study. Conclusion: One year of treatment with genistein improves surrogate endpoints associated with risk for diabetes and cardiovascular disease in postmenopausal women with MetS. Copyright © 2013 by The Endocrine Society.