Abstract: This invention relates to internally prestressed flexible capsule devices for insertion within or partly within the male and female urethra for the specific purpose of the automatic and/or manual control of urinary incontinence which is effected by a prestressed device deforming the lower interior of the urethra into a broadly elliptical shape stressed slightly in excess of the involuntary pressure, and such that the devices deform or collapse on their cross-section at the increased urine voiding pressure and open a free urine bypass cross-section area and when voiding ceases the capsule device returns to its maximum cross-sectional area for involuntary urine flow control ready for repeat cycles as selected.