To evaluate the prevalence of erectile dysfunction (ED) in hemodialysis patients and the effect of successful renal transplantation on it. Two hundred and seventy hemodialyzed patients underwent live unrelated renal transplantation from Sep. 2002 to Nov. 2005 in Sina hospital, Tehran University of Medical Sciences, Iran. Those who were younger than 20 years, positive history for diabetes mellitus, ischemic heart disease, hypercholestrolemia, pelvis trauma or prostate surgery cigarette smoking, previous renal transplantation and medication use with adverse effect on erectile dysfunction were excluded. Eighty eligible patients entered the study and were assessed by international index of erectile function, version 5(IIEF-5) pre and six-month post renal transplantation. The prevalence of ED in hemodialyzed patients was 87.5%. Aging had not statistically significant effect on it. There was no relationship between the duration of dialysis and ED severity. Sixty four patients had good functioning graft in 6-month follow-up and completed the study. Successful transplantation improved IIEF-5 score significantly (P<0.001). Pretransplantation IIEF-5 score, age at the time of transplantation and transplant artery anastomosis to common iliac artery had statistically significant association with ED improvement, while duration of dialysis had not. ED is highly prevalent in hemodialyzed patients. It improves significantly after successful kidney transplantation.