Since introduction of the PDE-5 inhibitor sildenafil 4 years ago, there has been a fundamental change in the treatment of erectile dysfunction (ED). Intracavernosal or intraurethral injections of vasoactive substances or penile implants as mechanical aids now play hardly any part in it. - The development of the PDE-5 inhibitors vardenafil and tadalafil prompts the question of whether and how these three substances differ in terms of their efficacy and adverse effects. - Sildenafil has proven to be a very effective medicinal product. Studies with a follow-up period of up to 6 years have been conducted. The success rate of sildenafil varies in the group of ED patients with an organic underlying disease from 43% in patients who have undergone radical prostatectomy to 85% in patients with a neurological underlying disease, and amounts to an average 82% (range 43-85%, 100mg). - In an evaluation of spontaneous reports of deaths associated with sildenafil, the FDA concluded that there was no deducible evidence of an increase in the mortality rate among sildenafil users compared to the general population. In fact, fewer deaths associated in time with the ingestion of sildenafil were reported than might have been expected purely statistically on the basis of the normal mortality rate for men in this age group. - According to the initial studies conducted, vardenafil and tadalafil demonstrate efficacy data approximately comparable to those of sildenafil. As yet, insufficient data are available to evaluate the adverse effects of vardenafil and tadalafil, particularly their long-term use and use in high-risk groups. - Sildenafil has already been used by over 20 million men in over 110 countries and is one of the best-studied pharmacological substances available. This adventage in terms of knowledge and safety data makes sildenafil a safe and reliable treatment for patients with erectile dysfunction.