['We studied adjuvant daily sildenafil citrate during and after radiotherapy for prostate cancer for erectile function preservation.', 'We performed a randomized, prospective trial of 279\xa0patients with localized prostate cancer treated with radiotherapy who received sildenafil citrate (50 mg daily) or placebo (2:1 randomization). Medication/placebo was initiated 3 days before treatment and continued daily for 6\xa0months. Before therapy and 3, 6, 9, 12, 18 and 24 months after radiotherapy patients completed the IIEF questionnaire, including the erectile function domain, the I-PSS questionnaire and the RAND SF-36®. All IIEF domains were\xa0scored.', 'At 12 months erectile function scores were better for sildenafil citrate than placebo (p = 0.018), 73% of patients on sildenafil citrate vs 50% on placebo had mild/no erectile dysfunction (p = 0.024) and the sildenafil citrate arm had superior overall satisfaction (p = 0.027) and IIEF total scores (p = 0.043). At 24\xa0months erectile function and IIEF scores were no longer significantly better for sildenafil citrate (p = 0.172 and 0.09, respectively) and yet overall satisfaction scores were higher (p = 0.033). Sexual desire scores in patients who received sildenafil citrate were higher at 24 months although they had completed drug therapy 18 months previously (p = 0.049). At 24 months 81.6% of patients on sildenafil citrate and 56.0% of those on placebo achieved functional erection with or without erectile dysfunction medication (p = 0.045).'] Does prophylactic sildenafil citrate improve select aspects of sexual function in men treated with radiotherapy for prostate cancer?