Sexual dysfunction impairs the quality of life of patients undergoing hemodialysis (HD). The aim of this study was to evaluate the prevalence and the nature of sexual dysfunction in a Moroccan cohort of patients with chronic renal failure (CRF) on HD. This cross-sectional study was carried out with a questionnaire in 86 patients undergoing hemodialysis. Clinical and biological investigations were done. The mean age of our patients was 46.27 +/- 15.68 years old. 81.4% of the cases suffered from a decrease in sexual activity after the onset of HD. The decrease or the loss of libido was noted in 59.3% of the cases. Total impotence was present in 22.1% of the cases and 36% reported partial impotence. Ejaculation was present in 86% of the cases. The comparison between the group of patients who had no sexual dysfunction (group I) and the group of those who had this problem (group II) showed significant differences of age, social status and sexual life before HD. Other significant differences were found regarding frequency of intercourses and sexual satisfaction. Group II was divided into 2 subgroups: IIA included patients who had sexual dysfunction before HD and IIB: those who developed it after. The comparison of this subgroups showed that differences were significant regarding age, weight and vascular risk factors (diabetes mellitus, atherosclerosis). Sildenafil was more efficient in the patients of the subgroup IIB. This study suggested that HD was one of many factors causing sexual dysfunction in hemodialysed patients. After this clinical evaluation of sexual dysfunction, we emphasize the value of a global approach of this problem. The use of sildenafil seems to be more valuable in young patients with erectile dysfunction which appeared after long dialysis duration.