Erectile dysfunction after radical prostatectomy is a major complication affecting postoperative quality of life. For early recovery from postoperative erectile dysfunction, attention has focused on penile rehabilitation using vacuum devices, prostaglandin E1 injection into the corpus cavernosum of the penis or transurethral administration, and oral drugs such as phosphodiesterase type 5 inhibitors. Phosphodiesterase type 5 inhibitors have been used clinically based on the results of animal experiments that showed a preventive effect on fibrosis and loss of intracorporeal smooth muscle. Small randomized studies had reported a benefit from penile rehabilitation using phosphodiesterase type 5 inhibitors after radical prostatectomy. However, the largest trial to date, carried out in 2008, failed to show that daily phosphodiesterase type 5 inhibitor treatment was superior to on-demand phosphodiesterase type 5 inhibitor treatment for erectile function recovery after radical prostatectomy. Thus, debate continues as to its efficacy in humans. Reports on penile rehabilitation using phosphodiesterase type 5 inhibitors have appeared after these negative results, and phosphodiesterase type 5 inhibitors are still widely used as first-line treatment in penile rehabilitation.