Erectile dysfunction (ED) is defined as the consistent inability to obtain or maintain an erection for satisfactory sexual relations. Data from the Massachusetts Male Aging Study have indicated that the prevalence of erectile dysfunction of any degree is 39% in 40-year old men, and 67% in those aged 70 years. Effective therapy has been available for some time, but it has commonly involved surgery, external devices or penile self-injection. For many men, these represent unacceptable barriers to seeking therapy. Recently, however, an effective oral medication has become available. This article reviews the physiology and pharmacology of ED. The literature currently available on the effectiveness and safety of various drugs used for ED is summarized, with particular attention to newly available oral agents. Guidelines for work-up and drug treatment of patients with ED are given. Detailed history and physical examination are crucial to the safe and effective treatment of men with erectile impotence. An extensive review of the literature shows that based on safety, effectiveness and ease of use, oral sildenafil citrate is an excellent choice for first-line therapy. Patients who use organic nitrates of any kind in any capacity should not be offered sildenafil. Based solely on effectiveness intracavernosal injection therapy remains the golden standard and should also be offered as an option for first-line therapy for the appropriate patients. Many alternatives are available for men who cannot use sildenafil or injection therapy. A thorough knowledge of existing medications is essential for proper treatment of ED.