With the earlier detection of prostate cancer and the increasing demand for treatment of organ-confined dizease, quality of life issues are becoming more important. Development of erectile dysfunction (ED) following radical therapy is a particular concern, and occurs in perhaps a third of patients treated by radiotherapy and 30-70% of patients treated by radical prostatectomy. Although it is assumed that the ED relates to damage to the nerves subserving erection, this view has been questioned recently and in at least a proportion of patients the cause appears to be vascular. Despite the likely cause of their ED, all patients presenting with ED after treatment for prostate cancer should undergo assessment by history and examination to ensure that there are no other correctable risk factors. Patients can then be considered for a number of treatment options, and currently sildenafil (Viagra, Pfizer) is usually used as first-line therapy assuming there are no contraindications, such as severe ischaemic heart disease or nitrate therapy. Sildenafil improves erectile function in 70% of patients with ED post-radiotherapy, but appears less effective in men after radical prostate surgery with a response rate of 40-50%. Other treatment options include self-injection or intra-urethral administration of alprostadil, and some patients are happy to use a vacuum erection device. Finally, if all else fails, patients may be suitable for penile implant surgery.