PURPOSE: We evaluated the efficacy of tadalafil for the treatment of erectile dysfunction after nerve-sparing radical prostatectomy. MATERIALS AND METHODS: From April 2004 to February 2005, 28 patients who underwent nerve-sparing radical prostatectomy agreed this study and were enrolled. The subjects were divided into 2 groups: tadalafil group(n=15) and control group(n=13). The tadalafil group started medication(20 mg, 2 or 3 times a week) when daily pad requirement was less than 1(pad-free point, mean 74th day postoperatively). Efficacy assessments included the score on the International Index of Erectile Function(IIEF), erectile function domain(EF domain) and Sexual Encounter Profile questions 2(SEP2), and 3(SEP3). Questions were administered in the preoperative phase, pretreatment, and 6 months post-treatment. RESULTS: The preoperative score for the IIEF and EF domain were 46.0 and 18.5 in the tadalafil group and 44.8 and 17.9 in the control group, respectively(p>0.05, p>0.05). At pad-free point, the IIEF and EF domain scores in the tadalafil group were 9.8+/-7.5, 2.7+/-2.7 and in the control group 10.0+/-6.8, 3.1+/-2.5. The scores were reduced significantly at the pad-free point compared to the preoperative phase, but there was no significant difference between the 2 groups. At 6 months after treatment, the scores for the tadalafil group were 26.6+/-18.2, 10.3+/-7.3 and had increased significantly(p<0.05, p<0.05). There was a borderline difference in the EF domain score between the 2 groups(p=0.085). Four patients in the tadalafil group(26.7%) and 1 patient in the control group(7.7%) could penetrate successfully. CONCLUSIONS: Although there was no statistical significance between the 2 groups, early tadalafil treatment after nerve-sparing radical prostatectomy may enhance the early recovery of erectile function.