A urethral stricture is characterized by a narrowing of the urethral lumen, causing functional obstruction.  Urinary obstruction can occur for many reasons. In particular, obstruction of urine, as it flows from the bladder through the urethra, may be caused by a narrowing caused by scar. It occurs rarely in women, and is seen more commonly in men. A number of things can lead to stricture formation, and the most important of these are: trauma/injury (straddle injury, pelvic fracture), infection (sexually transmitted disease), post-instrumentation (eg. traumatic catheter placement, transurethal surgery) and malignancy/cancer (rare).  Following injury to the urethra by the above methods, the scar may take many years to develop.  As such, a significant number of men will present later in life with an unknown etiology.