Results of a multicentre, randomized, placebo-controlled trial show that taking tadalafil while receiving radiotherapy for prostate cancer (external beam radiotherapy or brachytherapy) does not prevent erectile dysfunction. No significant difference in the ability to retain erection (according to International Index of Erectile Function score) was observed between the group of men who took 5 mg tadafail daily and those who received placebo, at 28–30 weeks or at 1 year. Sexual satisfaction and marital adjustment were also unaffected by daily tadalafil.