Testosterone (T) and its metabolites, dihydrotestosterone (DHT) and estradiol (E2) are metabolic and vascular hormones and regulate carbohydrate, lipid and protein metabolism. These hormones play an important physiological role in reproductive and sexual function, bone health, mood and cognition, vascular health, as well as body composition. Testosterone deficiency (TD; also known as hypogonadism) is a well-recognized medical condition with detrimental health implications. Testosterone deficiency is associated with several co-morbidities including metabolic syndrome, obesity, insulin resistance and type 2 diabetes, hypertension, inflammation, atherosclerosis and cardiovascular disease, erectile dysfunction, depression, dementia, reduced quality of life and mortality. Testosterone therapy treats various clinical conditions of testosterone deficiency with well documented benefits on sexual and bone health, anemia, glucose metabolism, body composition, depressive symptoms, mood, well-being, quality of life, and reduces overall mortality. Here we provide a summary on the negative impact of testosterone deficiency on human health and the impact of testosterone therapy in improving overall health outcomes and quality of life in men with testosterone deficiency.