To determine whether preoperative demonstrations of intracavernosal and vacuum therapies for erectile dysfunction (ED) influence the decision of treatment choice, reducing long-term regret. In all, 82 consecutive men with localized prostate cancer, scheduled for radical prostatectomy and reporting an International Index of Erectile Function score of >21, were prospectively enrolled at a single cancer centre. Following standard preoperative counselling, half of the men were invited to attend a further consultation for intracavernosal and vacuum therapy demonstrations. All patients were evaluated pretreatment and then 3 monthly using the five-point International Index of Erectile Function score and the 14-item Hospital Anxiety and Depression scale. At 12 months treatment choice changes were recorded and patients were assessed for treatment choice regret using Clark's validated two-item regret questionnaire. Statistical analysis was performed using the Mann-Whitney and Fisher's exact tests. Results were compared with a control population of 41 men who did not undergo additional ED counselling. In all, 8/41 men (19%) changed their treatment choice, opting for brachytherapy rather than radical prostatectomy. Only 1/41 in the control population changed their decision before surgery. At 1 year, one patient (2%) in the intervention group expressed regret at his treatment choice (radical prostatectomy) compared with eight (20%) in the control group (P= 0.03, two-sided Fisher's exact test); ED was identified as the major cause of this regret. Preoperative demonstrations of ED therapies can optimize decision making in prostate cancer and help reduce long-term regret.