Erectile dysfunction (ED) is one of the major complications after spinal cord injury (SCI) that decreases the quality of life of the patients. Although many efforts have been made to decrease ED, they are frequently cumbersome, with a high failure rate. The aim of this study was to assess the effects of sildenafil citrate at several doses, an oral agent that has been shown to improve a broad spectrum of ED. Sixty male patients with SCI were divided into 2 groups and received 25 mg or 50 mg sildenafil citrate, respectively, during a 4-week treatment period I hour before sexual intercourse. Our results demonstrated that sildenafil citrate significantly improved reflexogenic erectile response in both groups (P = 0.02 and P = 0.01, respectively). Subjects receiving sildenafil citrate reported that treatment had significantly improved their erections, frequency of sexual intercourse, satisfaction, enjoyment, sexual desire, overall sex life, sexual relationship, and self-confidence in erections (P < 0.05). There was no statistically significant difference between 2 groups regarding the dosage regimen (P > 0.05). The authors concluded that sildenafil citrate might be used effectively for the treatment of ED in patients with SCI, even in a low-dose (25 mg) regimen.