The increase of life intensity and its stressful impact, a great number of various risk factors of ED - erectile dysfunction and aging men population lead to a high prevalence and incidence of ED worldwide. It is well known that ED in men is a condition of heterogenous aetiology, which determines ED substantial diagnostic and therapeutic clinical problem. However, in most cases, ED may be managed quite well by the primary care physician who has proper understanding of the pathophysiology of ED. This article is intended especially for primary care physicians. It reviews physiology of erection and then explores pathophysiologic changes that are likely to cause inadequate erection, which enables better understanding of ED and consequently is essential for appropriate management.