The role of sex steroid hormones in modulating vascular function in men is of great importance, given that androgen deficiency is strongly associated with common medical conditions including metabolic syndrome, obesity, diabetes, hypertension and atherosclerosis. Testosterone deficiency afflicts approximately 30% of men ages 40–79 years. Testosterone replacement in deficient men with such co-morbidities ameliorates or partially reverses their progression. Studies in animal and humans suggest that androgen deficiency is associated with increased triglycerides (TGs), total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C). Emerging evidence indicates that androgens may provide a protective effect against the development and/or progression of atherosclerosis in men.