Erectile dysfunction (ED) is one of the earliest signs and markers of present or potential future endothelial dysfunction. One of the causes of ED can be low testosterone levels or hypogonadism. This article describes ways to identify and diagnose patients with ED or hypogonadism, and it offers a plan for treatment of these conditions. The mainstay first-line medical therapies for ED are phosphodiesterase-5 (PDE-5) inhibitors. For patients with symptomatic hypogonadism, testosterone replacement therapy is both safe and effective.