The phosphodiesterase inhibitors are first-line treatment for the most types of erectile dysfunction. Sildenafil citrate is the first and the most studied member inhibitors. However, research on the effectiveness and safety of sildenafil in separate groups of patients and continuing to this day. Such high interest to this drug caused by large heterogeneity of patients population taking sildenafil. Ерis article discusses aspects of the effectiveness of sildenafil in patients with chronic renal failure treated with chronic hemodialysis, and in patients who had undergone radical prostatectomy. These groups need to be further studied because they have objective decreased effectiveness of sildenafil. In addition, sildenafil is taking by increasing number of young and middle-aged men. Fertility issues might be crucial for them. At the same time we should not forget about the patients of older age groups, so the problem of the safety of sildenafil in patients with diseases is also important. Our analysis of the published data shows that sildenafil is an effective and safe drug that for trreating erectile dysfunction in the groups of patients mentioned above. This is true both for original drug and generics.