Abstract: The invention provides a sling prosthesis (10) for urinary incontinence and also a method of treating urinary incontinence. The sling (10) has a flexible elongate member (12) and a distensible portion (14) and is configured to be inserted dorsally between the urethra and pelvic bone, with ends of the elongate member attachable to retropubic or ischial structures. A valve (18) which is subcutaneously implantable in a labial or scrotal region may be connected via a conduit (16) to the dispensible portion. Fluid is injected via the valve into the distensible portion (14) to that the distensible portion (14) sufficiently constricts the urethra to inhibit undesirable leakage of urine. Fluid can then either be injected into or extracted from the distensible portion in order to alter distension thereof.