In an attempt to define changes in sexual function before and after renal transplantation, a questionnaire was distributed to adult male patients with functioning kidney transplants. Significant changes in sexual performance were shown during the transition from the healthy state to end-stage renal failure and, finally, to the post-transplant state. Both potency and libido showed marked parallel impairment with the development of end-stage renal failure, followed by moderate recovery after renal transplantation. This study indicates that the majority of men with functioning kidneys can look forward to a return of sexual activity comparable to pre-illness level. However, sexual impairment may persist in some patients after transplantation, emphasizing the need for further evaluation in this group of patients.