Localised prostate cancer is usually curable with surgery. Surgery often entails side effects of permanent impotence and temporary urinary incontinence. These side effects can be minimised by protecting the nerves that run in the outer layer of the prostate (nerve sparing), however this increases the risk of exposure of the underlying tumour (a positive surgical margin-PSM) and a need for extra treatment in the form of radiotherapy. PSMs are more likely to occur if the tumour is starting to grow out of the prostate (stage pT3a) and in areas where pT3a disease is suspected nerve sparing cannot safely be performed. At University College Hospital London (UCLH) the chance of a man being potent after radical prostatectomy is dependent on the amount of nervous tissue left behind. 80% of men in whom the nervous tissue is spared on both sides of the prostate would be expected to be able to get erections adequate for penetrative sexual intercourse using phosphodiesterase inhibitors (PDE5i's, viagra or similar). UK surgeons base a decision of whether to nerve spare or not on the degree of suspicion that pathological stage (pT) 3a disease is present, estimated from the patients prostate biopsies and MRI scan as well as a thorough clinical examination.