Incorrect drug administration, lack of sexual stimulation, the way of obtaining sildenafil and associating risk factors of erectile dysfunction like severe cardiovascular or neurogenic diseases were the common causes of initial sidenafil failure. To improve the therapeutic efficacy for patients with initial sidenafil failure, education about how to use sildenafil properly plays an important role. Moreover, dose titration, more attempts, a good follow-up and sildenafil taking on a daily basis will yield a high response rate to sildenafil rechallenge.