Detailed urodynamic and neurologic evaluation of 550 patients was reviewed with the intention of shedding light on the understanding of the neurophysiologic pathways involved in micturition. On the basis of our data the following conclusions were made: 1) normal micturition is a brain stem reflex rather than a simple sacral reflex, 2) interruption of this sacral-to-brain stem reflex pathway results in uncoordinated voiding (detrusor-external sphincter dyssynergia), 3) anatomically separate neural centers control the activity of the detrusor muscle and the external urethral sphincter, and 4) although the pudendal and pelvic nuclei are located in the sacral spinal cord they are anatomically separable from one another.