Erectile dysfunction (ED) profoundly affects the quality of life. The prevalence of ED in renal transplant recipients is reported by high as 50% to 60%. We evaluated the efficacy and safety of vardenafil in these patients with ED as well as its effects on graft function and on cylosporine or tacrolimus concentrations. Thirty-nine recipients with ED and serum creatinine values<2 mg/dL were treated with vardenafil. ED was assessed using the self-administered International Index of Erectile Function (IIEF). ED was diagnosed by using penile color-Doppler ultrasonography and intracavernosal injection. Vardenafil efficacy was assessed by readministering the IIEF questionnaire after 4 weeks of therapy. Serum creatinine levels, creatinine clearances, and cyclosporine/tacrolimus concentrations were measured before and after vardenafil therapy. Twenty-one recipients with ED served as placebo controls and 15 without ED as another control group. The IIEF scores improved from 12.80+/-3.5 to 26.46+/-2.4 in vardenafil-treated patients with ED (P<.001). Renal function and cyclosporine/tacrolimus concentrations did not change with vardenafil therapy. Side effects were observed in 7 (18%) patients: headache in three, palpitations in one, flushing in two, and dyspepsia in one. This study demonstrated that ED improved with vardenafil in renal transplant recipients with ED. For 4 weeks vardenafil therapy was free of side effects. Renal function tests did not change. Also, no dose change in immunosuppressive drugs was required during 4 weeks of verdanafil therapy.