There are a few studies published about unilateral anesthesia for day-case surgery. For bilateral anesthesia it was shown that recuperation of the detrusor function comes with the regression of the sensory block to the S2 dermatome . However, little is known about bladder function during unilateral block of the sacral segments, not to mention the detrusor function and micturition with an asymmetric recovery of the sensory and motor block.