The male urethra differs from the female urethra in that it is longer and more curved, about 18 cm long, and has a role in urination as well as sperm discharge. The male urethra has three physiological strictures: the internal urethral opening, the membranous urethra and the external urethral opening. The membranous part of the urethra is the narrowest, about 1.5 cm long, and is surrounded by the urethral sphincter, which plays an important role in controlling urination. Urethral stones are most likely to become lodged and obstructed at the three strictures. In clinical practice, when catheterizing, dilating the urethra, doing cystoscopy or inserting other instruments into the urethra, special attention should be paid to the three strictures and they should be operated carefully to prevent urethral injury.