INTRODUCTION: For all the studies into the sexual health of kidney transplant recipients, there is a paucity of controlled studies regarding the difference in the sexual relationship of kidney transplant recipients and end-stage renal disease (ESRD) patients under hemodialysis. AIM: We compared the sexual function of kidney transplant recipients and ESRD patients under hemodialysis in male patients. MAIN OUTCOME MEASURES: The patients' sexual function was assessed using the Relationship and Sexuality Scale. METHOD: In this case-controlled study, 89 male renal transplant recipients and 25 male hemodialysis patients were randomly selected from the outpatient clinic of Baqiyatallah Hospital, Tehran, Iran, in 2006. The two groups were not significantly different in terms of age, living place, level of education, duration of ESRD (months), ESRD cause, and somatic comorbidities (Ifudu index). RESULTS: The renal transplant patients in comparison with the hemodialysis group reported a better overall sexual relationship (17.3 +/- 0.6 vs. 21.6 +/- 1.4; P = 0.001), and all subscales including sexual function (9.9 +/- 0.3 vs. 11.4 +/- 0.6; P = 0.03), sexual frequency (6.3 +/- 0.3 vs. 7.4 +/- 0.6; P = 0.04), and sexual fear (1.1 +/- 0.2 vs. 2.8 +/- 0.5; P = 0.001). In addition, kidney recipients had significantly more sexual intercourse in a 2-week period prior to the study (P = 0.008). CONCLUSIONS: In our male population, kidney transplant recipients, in comparison with the ESRD patients under hemodialysis, reported a better sexual relationship.