Indwelling electrical stimulation of the pelvic floor by a radio-implant benefits some cases of problem or recurrent urinary incontinence. It is not possible to predict success or failure with a given patient. The only worthwhile criterion for selection is the presence of contraction of pelvic floor musculature in response to voluntary effort or trial electrical stimulation. The results are not simply explained by postulating electrically induced closure of the urethra. There may be conscious enhancement of the urinary sphincter mechanism. Re-education of voluntary sphincter muscles by electrophysiotherapy may occur. Reflex inhibition of the detrusor may occur. The surgery involved in inserting an implant restores continence in some patients.