The urethra is a tube connecting the bladder outside the body. The bladder can void urine through this channel. A stricture is a narrowing of the urethral calibre. Only when the stricture is severe, symptoms occur. 
Frequently the stricture is acquired, due to an inflammatory process with further evolution to scar. Common causes are urethral infection or iatrogenic (after transurethral  procedures).
Congenital strictures are rather rare.
Strictures of the posterior (membranous)urethra are usually post-traumatic, after pelvic bone fracture with tearing of the urethra. Strictures of the prostatic urethra are either congenital or acquired, after endoscopic or open surgery for benign prostatic hyperplasia.
The typical symptom of urethral stricture is a decreased urinary flow. Urinanry frequency and feeling of uncomplete voiding are not uncommon. In severe strictures recurrent urinary infections may occur. The urinary flow can decreased to urine dripping, or acute urinary retention can occur.
Urethrocystogram is the main test for urethral strictures diagnosis. A contrast medium is introduced in the urethra, and some x-rays are obtained. Once the bladder is filled, the patient is asked to urinate and new x-rays are obtained. All the urethra is visualized by the procedure, in retrograde and antegrade x-rays. The site, extension, number, and calibre of the stricture(s) are easily identified, to choose most proper treatment. Urethroscopy (introduction of a fiber optic in the urethra) has some diagnostic limitations, since it can show the distal end of the stricture, without any further information on the urethra beyond that point.
Once a diagnosis has been done, the first approach is often under vision cold knife urethrotomy, according to Sachse. The operation is performed under epidural anaesthesia, with a fiber optic instrument introduced in the urethra. The scar tissue of the stricture is incised under vision. The success of the procedure is depending upon the site and the extension of the stricture, and upon the clinical history.
For bulbar urethral strictures no longer than 10-15 mm success rate may exceed 70%. For strictures of the penile urethra, or strictures longer than 20 mm, success rate drops to 30-40%.
After the failure of a first urethrotomy, the chance of success of a second urethrotomy is very poor or none. 
In recurrent, long or multiple urethral strictures, the best approach is a urethral reconstruction (urethroplasty). Short bulbar urethral strictures are treated with stricture resection and end-to-end anastomosis of the healthy urethra.
Modern techniques use other tissues to reconstruct the urethra. A flap of penile skin, with preserved vascularization, can be used  Today one of the best options for urethral reconstruction is the use of a free graft of buccal mucosa, from the inner check or from the lower lip.
Success rate, even for recurrent strictures, is high (80-95%).
Recent experimental studies explore the possibility of obtaining urethral tissue through tissue engineering.