Sex hormones play a major signaling role throughout the body starting from sex differentiation in utero to senescence. While sex hormones are undoubtedly important for the development and conservation of reproductive health, their importance for nonreproductive function is now recognized in many organ systems because of carefully characterized experimental models and clinical studies. While testosterone (T) is considered to be the most important androgen in circulation and the main androgenic and anabolic signal in males, it may either directly exert effects on target tissues or be metabolized by 5α-reductase into dihydrotestosterone (DHT) or aromatized to estradiol (E2). Differential effects of T and its metabolites are not well known and are a topic of scientific debate. These pleiotropic effects lead to variable phenotypes, clinical manifestations, and significance throughout life and may be more pronounced in some systems (such as bone and reproductive organs) or stages (such as puberty) than in others. This chapter focuses on the available clinical evidence of the androgen effects on several important organ systems in males.